The newer bandsaws now have welded frames. They are lighter and just as strong, if not stronger. The industry standard 14" Delta saw had the cast iron frame and was cloned by many other "manufacturers" all over the world. It had the ability to increase the cutting height by adding a riser block between the upper and lower castings. It's limitation was that it was still a 14" bandsaw, BUT for many thousands of owners that was they needed.
The welded frame saws like the Rikon, larger Grizzlys, Lagunas are very popular and work great, but you better get the biggest saw you think you will ever need since no additional capacity is possible. I own a 18" and 2- 14" saws with welded frames and they work fine. The guides have also improved in the newer saws, with disc types in hardened steel or ceramic or ball bearings. Cool blocks were a choice on the old saws, but as far as I know, don't fit on the newer saws.
Kinda like cars have gone away from having separate frames and moved to unibody for structure, because it's lighter and cheaper. I had an old Craftsman 12" bandsaw that was made from 3 separate aluminum casting that were epoxied together, not welded. I even used it to cut mild steel with a 10 to 1 speed reducer and it worked fine.
Because of the popularity of the old cast iron saws, there will always be spare parts available in places like Ebay. Bearings on the drive or upper wheels are commonly available as are guide bearings. What else can go wrong? There should be no reluctance to buy older used machines that I see.