I know the magic number for the 500EFI valve spring change is 250 or so. I have a 2000 500EFI boat that had 170 hours on it when I bought it in March, just changed oil today showing 225. I think the boat had a pretty "easy" life before I owned it, and I certainly don't flog it by any means... however... will I be ok waiting till the end of the season to do these valve springs or should I consider the 250 mark to be an absolute worst case scenario and pull the boat down no matter what? Any opinions?

you can wait, ive seen 500's go 400-500 hrs

You will be fine. The 250hrs mark is just a good reference to start thinking about it, but plenty of people go 350hrs or more.

Ditto .... have you scanned the motors to see how hard the first 170 Hrs were?

A visual peek can sometimes reveal some broken springs.

Change them out over the winter. I use the Isky endurance springs. I got them from RMbuilder on the forum.

Mine are 2000's and I just cam in with 365hrs. I do not run mine hard cruise most of the time at 3700 rpm's/45 mph.
I think the 200/250 mark are for those who are running hard all the time and never get off the throttles, these are strong motors, just my opinion.