I'm with MikeB on backup - like now - if you've anything of value on the machine... sounds like you could lose everything any time now. Onto DVDs poss, or an external hard drive.
I wonder if there is a middle way?
I seem to go through the sequence you've described every few years: adding or replacing various bits with more reliable or tastier bits... and then suddenly realising that base units faster and more ambitious than mine are on sale on Ebay for a hundred quid or less. So I dump all my valuable stuff onto a hard drive, buy a new desktop, put the old hard drive - less programs & o.s. into the new machine as a secondary or tertiary drive and start the iteration all over again.
So why not get one of those 'last year' models for a few tens of quids, keep all the peripherals, and then wait as MB has suggested for the W7 dust to settle? Any extras you want to transfer to your interim machine can be stripped off old faithful, to do the things you need them for.