I think that would be a fine thing to do. It's always worth to look at the facts, and the fact says that it's not the AI who build most wonders who is too far away, but the AI that reaches new eras in advance. The difference in yields from handicaps is very noticeable even in King difficulty. I can only guess how strong it gets in higher ones. I know you want some epicness with some runaway adversaries, so if it flattens too much, you can always give a little more yields on events.