I would let you ride my WRX if we lived close, but we don't....So here's my $0.02 on the matter.
I've done all the standard performance mods, and it's much better than stock. The front will lift up now.
Fuel economy has dropped a lot. I get about 90 kms before the fuel light comes on. Stock, I was getting around 200 kms before said light turned on (Although my ODO is off now that I've adjusted the speedo). I don't care about the extra money, I just hate having to stop at gas stations multiple times a day on big rides...
I've gone to 13/48 gearing and my top speed is now 130 km/h (I didn't buy this bike to do top speed, but this gearing makes highway use a pain to keep up with traffic).
I have NOT done any suspension work, as I like a softer ride. It has worked well for my riding style/preference while offroad (fireroads/dirt roads/trails/small jumps/etc).
I love the "zero maintenance" of the WRX, but honestly I'm looking to trade her in for a new Husqvarna 701 Supermoto this Fall (KTM 690 SMC-R drag queen).
The WRR/X is a great 250, but it's still a 250 and it'll never have the performance of a big bike.
I have friends with bigger bikes (KTM 625 SMC/KTM 690 SMC/Husaberg FS650e) and the difference is astronomical.
That said, if you really like the bike and want to keep it, do the mods as they really do improve the performance.
If you're on the fence between modding and keeping the bike or changing for something with more power, I'd say save your money for a different bike.