Should I re-rip?

I doubt you'll hear a difference between WAV and flac. I have what might be considered a better than "average" system resolving capability and can't hear one. 
Default settings probably meant the amount of compression. Doesn't affect sound quality, just the final file size. 
Bottom line, IMHO not worth the effort if it's a lot of CDs.
There's sure to be other opinions.

FLAC is a much smaller file than WAV. So, before you head that direction you need to answer two questions: (1) how much storage capacity do you have? and (2) how much storage capacity will all your files in the WAV format require? I agree that the default settings for FLAC via dbPoweramp  is probably fine. I do suggest you do one CD into WAV and compare it to your FLAC file. If you hear a difference and you like it, then I suggest you rip another one and see if you still like it. If you go 2 for 2, then I suggest you have someone else run your server and pick the version you listen to without telling you. If you can discriminate the difference between the two, and you pick the WAV consistently as your favorite, then you have some decisions to make.

WAV is preferred only from the perspective that it is uncompressed and has an advantage over flac during playback because, unlike flac, it does not have to be decompressed. That said, best of luck attempting to discern an audible difference.

FLAC is preferred from the perspective of being compressed and, therefore, taking considerable less hard drive space. Do not concern yourself with the flac compression level you chose during the RIP, because whether you chose max or min or somewhere in between the resulting file size will be nearly identical.

As to metadata, FLAC is preferred (i.e. can accommodate more attributes) to WAV.

As to Steve Nugent recommending AIFF over FLAC, not sure why, but best of luck if you attempt to discern a difference.

As to dbPoweramp settings, here is where you could have gone awry. There are different RIP options having to do with error correction. Usually, people are in a rush and software defaults to what is known as "burst" mode. That essentially means RIP quickly regardless of any error(s) encountered. The better mode is referred to as "secure" mode, which essentially means take all the time necessary to re-read a disk if error(s) are encountered. Exact Audio Copy has a mode known as "paranoid" mode, but I won’t even go into that :)

In short, you probably do not need to re-rip your CDs. But depending on how many you have, and whether or not you’re "paranoid" (pun intended, but it’s literally a mode in which you can rip), undoubtedly this will guide your decision.