Finding 940 parts ought not to be difficult, as they're often ravaged for their engines and other parts. Sedan doors do fit wagons.
Heater cores are available ex-UK. It's a long and fiddly job to do, but once done, it's done.
Compressors for a/c do fail after 25 years. Replacements are easy to find brand new for not a huge amounts of money - look for the correct compressor make and model by that criteria, and then you avoid the Obligatory Volvo Price Hike.
Window regulators may need to be cleaned of 25YO grease and re-greased - did this with mine after similar issues, and all is good.
It's inevitable quarter century-old cars are going to need attention of some sort.
As to the 700/900s not ever achieving the present 240-like cult status, I'm not so sure; it's only recently (last two years or so) that 240s have achieved it; it may be Sevens and Nine will take a little longer to get there. They are, after all, the last of the RWD Volvos.
Funny thing though - at the Oz Volvo Nationals in Taree years ago, a gentleman offered me a very generous amount for my 93 945T and I turned him down, and this was before the car had been tidied up. I don't regret not letting it go; for what it is. While not particularly sexy or trendy, it's a good, strong, reliable, comfortable daily that that turns, stops and goes better than present-day gerlytrucks and which is enjoyable driving cross country (no pun intended), COVID lockdowns and barge restrictions permitting. LH2.4 has enough smarts to diagnose issues without being a Hitler-like CAN bus, and it still has enough puff to blow the Korean road gnats into the weeds without raising a sweat or excessive thirst, while carrying a good sized load in comfort. So, yeah, I'm a 940 fan, and I'm keeping mine. :)
Up to you if you want to scrap a running car that needs a little attention. IMO the value of your complete running car is more than the cost of items need to do a +T on a 240.