Depends on how much money to want to spend. Reading some of the Crackheads impressions of the affordable film caps ... Solen, Axon, Mundorf etc. Most, if not all, felt they were a worthwhile improvement. Most seem to agree on a smoother treble, less "grain" in the upper mids and treble. Perhaps a tighter bass. You read about midrange "glare" from a lot of reviews for some of the affordable film caps in those crossover reviews. Nobody seems to report that in this application. I dont hear any at all with the Mundorf MKP's. By all means, spend as much money as you wish on film caps. Im sure there are sonic benefits based on indiviudal preference. But from what I have read, I would not completely rely on the reviews of the caps in speaker crossovers as an indicator of the same performance as an ouput cap in an amplifier.
I think that the Mundorf caps were well worth it and would do it again in a second. I got them during a 20% off sale too. But the stock electrolytics arent bad at all. Outside of the now gone Blackgates (NP's), I dont know of any electrolytics that any type of concensus would consider an upgrade over a film cap. There is Jensen and, I think Mundorf, that have some, supposedly, higher end electrolytics that could be worth trying. Dont know of anyone who has tried them in Crack. Since you are leary about improvements over the stock lytics, you could consider trying the Axon 91uf (Percy has them I think). Very reasonable in price and if you like them, then maybe consider trying "boutique" films. Seems like Axon, Solen and Mundorf MKP are all "safe" bets for improvement based on cost and feedback here on the forum.