It's a really difficult one, this. I think I'm torn between two, equally valid theories.
1 - Get the best out of your equipment that you can.
2 - Bring up some grey ramps on a test disc. If they look like they're tinted, rather than varying shades of black, grey, and white, what makes you think you'll notice it in a film?
Truth be told, both are right. And then trhere are other factors as well.
Very bluntly, if you've spent £5k (or more) on a projector, you'd be daft to not pay what is effectively just a few bob more on a calibration. If you've only spent £600 on a projector then you'd probably have been better off getting a £1k projector. Anywhere between £1k and £5k...it's up to you.
Just remember, a £350 calibration is over 20 new Blu-ray Discs. And ultimately it's all about the films. For me, I'd rather watch 20 great films on a poorly-calibrated display than no good films on a well-calibrated display.
But then again, I'd rather watch hundreds of superb films on a perfectly-calibrated display.
Steve W