You probably wouldn't see much of an immediate increase, but it would likely improve your scores over the longer term from a more seasoned account mix -- particularly if your overall credit history is young. (I expect we're talking single digits, unless you only have 1 or 2 open accounts at present.)
In addition to the benefit of increasing your average account age, available credit on the accounts would lower your overall utilization - also improving your scores. (But you can get that benefit by opening any new account.)
Note: many creditors won't reopen an account once it's been closed -- merely consider you for a new account.
Once reopened, the accounts need to be occasionally used so that a statement is generated (you can pay in full) -- say once every 6 mo to 12 mo -- to avoid the accounts going inactive.