So will any future bugfix releases for v0.34 break savegame compatibility post v0.34.05?
Depends on how you define breaking save compatibility. Actually preventing a player from moving a fortress to the new version? Extremely unlikely. The reason compatability broke between 34.01 and 34.02 was there was a very nasty bug in 34.01 that corrupted your worlds and made them unplayable after a while; Toady manually put in a compatability break to discourage people from using that version. To the extent of my knowledge, that's happened
once in the six years or so since the first public release (although some bugs certainly were almost as bad. The "press K to crash the game" bug comes to mind).
The other reason total compatability breaks happen is when part of the game becomes so fundamentally altered that Toady can't realistically make a fix that ports old forts over. This has happened 3 times in the last six years, and only in major feature updates.
As for the times where you can upgrade your fort to a new version but some bugfixes and new features won't be there, those are fairly common. It looks like most of the clothing bugfixes are changes to the dwarf AI, though, which should generally work in forts ported to newer versions.