It depends and only you can answer. I was in the same boat but I already had the wider arms, axle and shocks but stock engine. My engine was needing a freshing up so I made an offer on a leftover 05 model 450R and they wouldn't take it so I decided to spend the money on the EX (of which she needed a little engine work anyway)

I'm glad I kept my EX.

I don't need the higher HP of the 450's and my riding areas suit me fine. Maybe if more of my mods would've swapped I might have raised my offer but I would've had to purchase new arms, axle, rear shock and I didn't care to spend that much.

For about $700 I have an engine that runs right with a YFZ (I raced my first one this weekend) for about 100 yards (only room we had)

Good luck in your decision and I guess the main thing is are you willing to part with the money?