I think that this depends of what kind of game it will be. In an Action-RPG we do not want to care about such things like ‘realism’. But in a Classic-RPG we can be able to notice more details of realism.
Since very few games have gold limit, nobody will notice if the gold has no weight. But if you would implement such limitation, you will need a good justification, and if the system works fine, it will have make history again because weight always got sense.
Gold limitation must be supported for a balanced loot system, i.e. you will don’t want to have the necessity of exchange gear frequently, in this case, gear doesn’t need to stay in inventory all the time, also a craft system could solve the excess of items (like melt 10 swords to forge one better), it also needs good trade rules (the best sword can’t cost 1.000.000 times more than the cheaper one like in ARPG games). Etc. With simple rules well applied, gold can have weight and players will not miss anything.
Imagine the following. Player 1 is not a very hardcore RPG player and merely picks up gold he finds in the world, e.g. after battle. He's a friendly guy too and doesn't ask quest-givers for rewards. He spends most of his money on potions because he's not that good in combat.
Player 2 on the other hand, opens every barrel and crate there is in the world, talks quest givers into giving him rewards, has a pickpocket skill maxed out and robs traders blind, and picks up and sells everything that's dropped after combat or that's just sitting there in the world. He even goes back for loot if picking everything up at once is impossible.
Well, games who want to stay ok with all kind of players are often called casual. In most of cases you will need to choose what kind of players are you targeting.
And if you will implement difficulty settings, please: reward the effort! Since in most games people who ends in easy will have the same rewards that the ones who play in hard, but in less time, and this is a little unfair.
effective attribute and skill levels dropping proportionally with damage taken
This is another topic but I want to say that this is a good idea to notice that the health bar is much more than a simple bar.
