Not just no, but Hell NO!!!
It's bad enough when everyone has to save every copper so that they can go down to MageMart and buy their next +1 upgrade (which I was hoping this next edition was moving past)...I certainly don't want to move from that to saving every copper so that I can buy actual experience/levels...
Coinage should NOT be directly convertible to personal combat power (that was the problem with the MageMart, and buying levels is even worse)...Money helps you to win friends and influence people (or buy ale/whores, minstrels, jewelry, castles, or make donations to your church or other charitable gifts that befit a would-be hero, etc.)...I don't want my character to gain a 1Up for every 100 coins he collects...This isn't Super Mario Bros....
Your character should get xp for things other than combat, sure (you should get the exact same amount of xp for sneaking past a mob, negotiating with them using diplomacy, or slashing them to bits)...But you shouldn't be able to simply buy xp/levels with treasure...
Your character's economic status shouldn't have any effect on his class level...It would be nice if a young noble could begin his adventure alongside a pauper thief without having to artificially limit the noble's wealth due to the ability to directly trade gold for magically enhanced equipment and extra class levels...
I don't want a situation where for all practical purposes only wealthy people can be high level and all high level people are necessarily wealthy...
I want Bilbo and the Dwarves to be able to find Smaug's treasure horde without being pressured by the system to buy themselves up to Epic level and go down to the corner store and buy sets of +5 equipment for everyone...And I don't want the system to basically dictate a minimum level they would have to be before they are allowed to find said horde...
Just my 2 cents (on second thought, I probably should save those to buy some xp)...