BOE, Ostfront and The Last Days are the 3 DGen campaigns payware add-ons. IMHO BOE is worth it, then Ostfront as well. Regarding The Last Days... it contains a lot of bugs - I know fairly well because I spent a lot of time to correct various files to make it work and which are included in EnjoyR patches - and even if bugs are corrected - with EnjoyR patches - the content is such that I almost never played campaigns included in The Last Days.
All other payware add-ons are, as far as I know, static/scripted campaigns. However you can find a lot of great freeware campaigns of a very high quality at M4T, and finally you may never play these payware campaigns.
Bottom line IMHO: add just BOE to your game, since it is required even to play some freeware DGen campaigns, plus EnjoyR patch for BOE, plus all EnjoyR skin patches, plus the freeware scripted/static campaigns you like from M4T, plus the freeware DGen campaigns you like from M4T, and you can play for years without going into the payware stuff, except for BOE.