I am in accord with nearly all this thread.
I sell a lot of sleeved guns which give people with more modest means a way of owning a really nice gun but at a huge discount on one with fine, original barrels.
My first Blanch was bought with sleeved barrels and it is my wet weather gun to this day (and I am very fond of it).
I am with Digs on this one: if the action is a beauty then restocking and/or rebarreling/sleeving is a very serious proposition.
I recently bought in a well-used, early 12g H&H Royal. The barrels were toast but the wood and action were good so it needed re-barrelling or sleeving. Re-barrelling was really not economically viable so I sleeved it, but to 16g! Now I have a really nice antique, 16g SLE with 30" tubes and balance to die for. It was destined for the stock list but I'm tempted to keep it for my own use for a while!
I also have my father's J Blanch & Son back action SLE. Due to poor antique workmanship on a repair, there is a very thin patch in the left tube and it really needs to be sleeved. However, I am planning to keep the lovely old, but thin, damascus tubes intact and have the gun rebarrelled in 16g chopperlump, strictly for my own use. It may not be a valuable gun but the combination of a family hearloom, fine wood that fits and a beautifully engraved action make it worthwhile for me.
Old guns with issues are only constrained by ones imagination and depth of ones pocket!