Well I hope this question doesn't devolve into another war where one side says 'THX is just a money grab with no real benefits' and the other side says its the greatest thing since sliced bread.
The truth lies somewhere in the middle. True, manufacturers pay for the certification but certification ensures the receiver meets some fairly stringent criteria. Many non-certified receivers can meet the requirements even though they haven't been certified so IMO the choice comes down to whether or not you think the THX specific post-processing routines will be of any use to you (re-eq, timbre matching, adaptive decorrelation and THX-EX (5.1->6.1).
If you can handle the price difference it might be useful to go for the THX certified receiver so you would have those features and can try them out to see if they make any difference to your ears in your room. The extra power can't hurt either. So is slightly more power and thx post-processing worth an extra $175? That is something you will have to think about...