Usual links
X-Wing guide to installing and playing: http://s93768914.onlinehome.us/xwing/
Module download page: http://www.vassalengine.org/wiki/Module:Star_Wars:_X-Wing_Miniatures_Game
Tip jar: http://s93768914.onlinehome.us/pub2/500release/index.html

Cliffsnotes of what's new with this one?
5.7.1's micro release happened recently, and added the "Bombs Away" preview article cards related to the TIE Bomber.
This new 5.7.2 micro release adds the newly spoiled TIE Defender pilots from the "Defend the Empire" preview article, as well as the TIE Shuttle title upgrade card (which I forgot to replace, last update)
New: Glaive Squadron Pilot (TIE Defender pilot)
New: Countess Ryad (TIE Defender pilot)
New: Maarek Stele (TIE Defender pilot)
Swap: TIE Shuttle (title upgrade)
The swap doesn't require any work on your logfiles that used the TIE Shuttle card. The art is simply automatically changed for the new one, if you download this new module.
I you care about having 100% of Imperial Veterans now (except the mission tokens, but LOL who cares right?), get this 5.7.2 module.
Why make a whole new version (again) just for 3 new cards? What a hassle!
Dunno if you checked recently, but the activity on Vassal X-Wing is nonstop now. There are multiple huge events (biggest being the Vassal League from earthworm, sozin and co). The players in it profit regularly from accessing bleeding edge content previewed by FFG, which allows X-Wing Vassal to be on the cutting edge of the upcoming meta.
Technically, if you don't download 5.7.2 (and/or didn't download 5.7.1) and keep with 5.7.0, it won't matter much. Only the 5 new cards won't appear from your point of view. Most players are accomodating when module versions mismatches are creating issues - easily solved through a quick discussion!
Nothing else has changed in the module, so your 5.7.0 logfiles are perfectly okay to use, despite the warnings of version mismatch you'll get from Vassal. Just ignore those warnings completely!