Even if you upgrade, why would you have to rip your songs again?
Again - suggest do the test - and actually learn your own limits.
Use lossless for archive purposes (so you only have to rip once) - and also use for PC based listening (makes sense when space is not an issue)
Use lossy for portable based listening (ie transcode either separate copy - or transcode on the fly through iTunes). That way you have more space - and you won't be able to tell the difference anyway. Just set-up iTunes to transcode to aac256 automatically when transferring to the iPod.
EDIT - BTW transcoding is very simple. Try dbpoweramp - can use multiple cores, and transcoding a full album takes well under a minute on my PC.