Thoughts on replacing caps in 30 year old speakers

Why not.  Projects are fun and you derive satisfaction from hearing the distinct improvement.  Would not go nuts with Mundorf and Jorma internal wiring, but within reason it's a good idea.

Sure, there's always room for improvement in any commercial design, but keep the old parts in case you don't like the sound.  It will sound different, not necessarily better.

I think you'll be surprised and very pleased.  However, Theil made some bitchin' difficult and complex cross-overs, so good quality stuff will be
expensive just due to the parts count since a single good big cap can run $80 or more, so...

Around 40 caps per speaker . Solen . Could just redo with solen . Biggest cap priced out around $10 . Have zero experience with speaker building , can the solens be easily improved upon ? With the costs being reasonable ?

From my reading it is the electrolytic caps which deteriorate with time and change value.  If your crossover contains any of those they will be the candidates for replacement.

"Upgrading" any other caps will more likely be a matter of taste.  As rcprince suggested, it may not necessarily be better than what the speaker designer chose.