I tried to look up the definition of 'hinky'...no success, LOL...
I'm not completely sure what your problem is...but some of this may help you pin it down, or give you info to post back here for better help.
1) I hope you reinstalled the zune software, not hardware on your 'scrubbed' PC. However, if you log into the same zune account and you linked your zune to the reinstalled zune software, your pass should work fine, your purchased music should work fine, etc. The software should manage your collection and sync according to whatever your sync settings are now...it would only 'not' manage stuff it thinks is from another PC...but logging in and linking would put the software (if set to smart sync) on this PC in charge of collection management.
2) You can redownload protected (which are all wma) files from the marketplace a handful of times, unless of course, the marketplace lost the license to sell those tracks. You cannot redownload unprotected (MP3) files at all.
3) It is possible the record label for Neon Blue decided to stop offering tracks and only offer full albums. MS has no incentive to do that...but they have to abide by the contract with the supplier.