I've heard opinions either way, but for some masochistic reason decided to ferret out the cold hard facts.
Warning - the following post contains math.

Wisdom levels
1 ) 2% experience bonus, clvl 6
2 ) 4% experience bonus, clvl 12
3 ) 6% experience bonus, clvl 18
4 ) 8% experience bonus, clvl 24
5 ) 10% experience bonus, clvl 30
From this
web page on
Divine Divinity's site, the experience required for each level is;
E = 1000*(level^3 - level)/3
If you put a point into Wisdom at level 6 (70k exp), you will get a 2% bonus. To get to level 12 you need (572k - 70k) = 502k experience, but due to the bonus, you only have to earn an additional (502k / 1.02) = 492.16k. This means you would reach level 12 after earning (492.16k + 70k) = 562.16k experience points.
In this context,
earned experience means experience not counting any Wisdom bonus.
Doing the same for each Wisdom skill level, you can calculate the required earned experience to reach a specific experience value with Wisdom bonus. If you graph the results of experience with Wisdom (Ew) versus earned experience (E), you would end up with a set of 5 connected line segments with slopes of 1.02, 1.04, 1.06, 1.08 and 1.1 (excluding experience for character levels less than 6, which would just be a line segment of slope 1.0).
The appropriate values are (in thousands of experience points);
Level (Ew) | E | Ew | |
6 | 70.00 | 70 | |
12 | 562.16 | 572 | |
18 | 1875.62 | 1938 | |
24 | 4386.94 | 4600 | |
30 | 8451.75 | 8990 | ** E0, Ew0 |
30 (E) | 8990.00 | 9582.07 | |
The first line is at the start of level 6, before Wisdom comes into play. The next 4 lines show how much experience must be earned in order for that value plus the Wisdom bonus to bring you to levels 12,18,24 and 30. The last line indicates that if you earn enough experience to get to level 30, the Wisdom bonus will
not be enough to get to the next level (9920k). That fact is used implicitly in the next calculation.
When does the Wisdom skill actually pay off?Let's say you have earned E experience, which is dE more experience than you had earned at level 30 (call this E0, the value in the line above with the '**' ).
dE = E - E0
with the Wisdom bonus, this increase in earned experience results in an additional
dEw = 1.1 * dE = 1.1 * (E - E0) = Ew - Ew0
of experience points.
At some point the earned experience points E will correspond to a character level L.
E = 1000*(L^3 - L)/3
Assume that the experience bonus from Wisdom is enough to bring you up k number of levels, to L+k, where L and k are both integers.
Ew = 1000*[ (L+k)^3 - (L+k) ]/3
If you substitute these equations into the two above, you get an equation in terms of L and k, which can be solved numerically.
When do you get one extra level?with k = 1, L = 37.41
If you earn enough experience to reach level 38, the Wisdom skill results in an a bit more than one extra level.
When do you get two extra levels?with k = 2, L = 64.14
If you earn enough experience to reach level 65, the Wisdom skill gives you a tad more than two extra levels.
Conclusion;Unless you go completely insane using resurrect on the dragon riders at the end of the game,
maxing Wisdom will only result in one extra level. It takes 5 skill points, and gives back one skill point and 5 stat points. Leveling up will be a little faster, though.
If you have nothing better to put skill points in, this is a fair trade. When I started, I kind of assumed Wisdom would eventually have a better pay off, but with so many spare skill points, I can hardly complain that it was a huge mistake. At the end of the game I had 10 un-used skill points, even after maxing one skill I didn't use and topping off a few I didn't need. If you would use those 4 skill points (net) elsewhere, don't bother with Wisdom. Most of the posts I recall seeing from people who have finished the game, though, have mentioned having skill points left over. They would be better used in Wisdom than not at all.
Any points in Wisdom will help, it just may not result in a full level increase. Each level you go up would come a little bit earlier in the game than it would otherwise, which could potentially come at an opportune moment. Also, if you find something with wisdom on it, you don't have to trade a skill point for the bonus experience. A low level of Wisdom might not be enough to result in a full extra character level, but it could get you a level higher than you would have been. For example, if you earn enough experience to get to level 49 and just a hair more than two thirds of the way to level 50, Wisdom level 1 would be enough to get you up to level 50. Not a huge difference, but it could help out a bit at the end of the game.
BTW, if you ignore Wisdom until level 30 then max it, earning enough experience to get to level 45 will be enough to get an extra level. With the 5 level jump on becoming the Divine One, that is not vastly different than level 38 (from always increasing Wisdom when available).
If you missed putting a point in Wisdom right away when leveling up, there is no need to kick yourself over the 'lost' bonus experience.
one more thing...
4 skill points (net loss) could be considered a lot to give up.
Do you need to max Wisdom to get any benefit?The great thing about graphics calculators is that you can change a couple constants to variables, and solve the equation above for L and k assuming any level of Wisdom.
If you put skill points in Wisdom up to a certain level, then stop, when will it be enough to gain an extra level (k=1)?
Wisdom Level 1, L = 151.01
Wisdom Level 2, L = 76.16
Wisdom Level 3, L = 51.91
Wisdom Level 4, L = 41.44
Wisdom Level 5, L = 37.41 (to re-cap)
With Wisdom at level 3, you need to earn enough experience to reach level 52 for it to result in an extra level. This would put it very close to the end of the game, or past it, for most people. Level 3 looks like a waste of skill points.
With Wisdom at level 4, you need to earn enough experience to reach level 42 for it to result in an extra level. This is a little later than level 38 (for a maxed Wisdom), but certainly early enough to be useful. You may not get much benefit clearing out the Dark Forest, but you would by the time you become the Divine One.
At level 4, you would have a net loss of only 3 skill points, and an extra 5 stat points. This could be considered the sweet spot, depending on how many extra skill points you have; almost the same benefit as maxing Wisdom, but costing one less skill point.