Not to be contrary, but the last line of the summary in the wiki article is:

The hedonic treadmill viewpoint suggests that wealth does not increase the level of happiness

I would infer from that, that increased wealth has increasingly diminishing returns after a certain point.

I did try to follow the link, but Investopedia broke it on their end and I can't seem to find it (aside: wooof, that is a bad layout). Any good sources for me?