I believe the next one "Colony Wars" which releases in 2 days is worth it, as it is a full blown Set like the ones in Ascension, not like the Crisis: Expansions which are a glorified promo-deck if we want to draw comparisons again with Ascension.
To the worth of the mini-expansions:
Gambits: not liked much in a tournament setting, but aside from that the most value for money (most new cards included (gambits + all promo Cards Year 1)
Gambits are dealt at start randomly to players and can be used either one time only, while some have a lasting effect.
Spice things up really good, but can be a bit unfair to what gambits you are dealt. But against AI or non-tournament games they are great
Crisis: Several subsets sold and implemented seperately
Crisis: Fleets & Fortresses and Crisis: Bases & Battleships:
More of the same, no new mechanics
Something like "purchaseable gambits" Heroes can be purchased like bases and put directly in play and have a one-time use effect when scrapping them
Cards which are in the Purchase deck and have random effects which are dealt the moment they are unveiled by purchasing cards
if you only want to get One go for Gambits. if you want some more go for Events and Heroes next. I like B&b and F&F but they bring the least new stuff to the table. But I would over time get all of them. You can individually enable them much like in Ascension.
For example my longtime opponent/nemesis @kennfusion and I are playing concurrent games with everything enabled aside from gambits. Its fun I believe.
More detailed info here
Speaking of which, now I knew why you didn't challenge me again after our last match. I was puzzled by the missing rematch request, now I know whats up....
FINALLY COLONY WARS!