I did the musical pub crawl a few years back: it was Ok, but I'd agree, more for tourists than for serious folk musicians! I think we had 3 pubs, time for a half in each only, but got quite a lot of Dublin history on the way: but we were not invited to sing then.
Serious (or even not-so-serious) musicians prob better advised to find a good session - for which there are other threads on this site.
The tourist bus is also good value -for tourists - the floozy in the jacuzzi, the tart with the cart (or the mish with the fish) remain in the memory!