In my experience, in the top shows each season, the talent of the original cast is on a different level than most replacements and touring casts. Not necessarily to say that the actors replacing the originals are less talented, but they are often directed to fit the original actor's outlines and are often less experienced. Additionally, there are stars and favorites who I specifically want to see onstage. So - yes, when I can take advantage, I try to see the original casts in the new shows. Since I live on the other coast, I usually can't revisit a show to see a replacement performer, or more accurately, new shows have a higher priority than replacement casts in shows I've already seen.
As for tours - yes, the casts in the first-class tours are usually excellent - and fully equal to the replacement casts on Broadway. Luckily in SF, most tour productions are Equity, 1NT-level shows, so the experience is solid.
But when filling the slots for a NY trip, I look for the OBC.