I would suggest you to try those expansions and you will probably get an everlasting pleasure with UB and Wildfire 6.0. Just wondering whether I am really objective...
There are a lot of changes regarding the guns in both sequel; nevertheless Unfinished Business is quite short as you get approximatively only 15 sectors or so...IMHO the best one is Wildfire 6.0 (not the hugely bugged Wildfire 5.0 from Strategy First which is not supported anymore by the developers) edited by Zuzzex. New guns, 10 new hireable mercenaries, big changes in every sectors and numerous enemies, etc... My team has been smashed several time even in the first sector; a true challenge mate!!!

leure:
If you speak fluently german, go ahead...

as I get this version. AFAIK the english version is only available in Czech Republik and there should be some website where you can purchase from; unfortunately I don't speak czech so was unable to fullfill the order...

leure:
Regarding the future development for JA3 , I don't know anything.
Give just a try to the demo of Brigade E5: New Jagged union, it is quite interesting although it is in 3D and using the "smart pause mode" instead of the AP system. Guns and ballistic seem perfectly modelized compared to JA2.
However I am still questioning about the campaign mode à la JA2 or the game only includes a serie of missions...
Hope this help.