As a follow up to my brief answer to get the ball rolling, I would certainly think long and hard about it, as I have enjoyed this hobby for over 30 years now. My biggest issue is that I have grown bored of the new stuff these days as many of you have. I started in a simpler time, when I had one set to choose from each year, unless I went for other sports or non-sports. There were a number of choices across the entire card collecting arena, but as for baseball, it was Topps. Later the choices became greater and greater and I fell victim to the "have to try everything" sickness that the card makers hoped we would.
I have a bunch of stuff that I like, but it is overproduced and would be easy to replace. I am not sure I would care to in a rebuild though. I have most of the oddball sets of the 80s and 90s, but wouldn't feel the need to replace them. I like the items that many don't pay attention to...postcards, team issues, newspaper inserts, etc. I use to say if you couldn't get it in a pack, then I wanted it! However, with the newer issues, it is nothing special for the most part. Sure, the inserts were shiny and die-cut, etc, but it just got old. Even now, when I look through boxes of stuff, I marvel at the Frank Thomas cards I gathered, but my real joy is going through the vintage boxes! Even with the low serial numbered items, if that was my passion, I would return to rebuild no questions asked if I cared that much about the new cards.
My favorite area of collecting, besides my player collection (which alone drives my collecting passions these days), is Dodgers and autographed cards. I have been picking up stuff at shops, shows, mail order and ebay for many years and was lucky enough to start early enough to land many great items that have since become much harder to find. For example 1958 Bell Brand cards, 1950 Drakes, 1953-55 Stahl Meyers, 1954 Wilson Franks, etc. These are just downright expensive and hard to find these days. I also have gathered up a nice Dodger autograph collection. I have most of the key players and those would also prove painfully expensive to replace. The thought to re-buying items I already had, at premium prices, just sickens me. The autographed cards are somewhat replaceable, as I have a number of newer certified issues, but finding a new 1956 Topps Karl Spooner, a 1955 Gil Hodges or a 1933 Goudey Willis Hudlin would be a far cry harder, if even possible. Those older cards feature mostly deceased players who I could not reproduce on my own and would have to rely on sellers offering up those types of things, again!
I would miss collecting for sure, but I know I would not have the means or passion to build back what I lost.