regarding life span of tape, and of time-span of optimal tape playback; not all tape is created equal. I'm an amateur with only anecdotal experience but I have about 150 master dubs all done with modern tape formulations. quite a few of them are now going on 7 years old, and some have been played many dozens of times with zero apparent degradation.
possibly part of the issue is that I play my tapes exclusively on a pair of Studer A820's which do have remarkably gentle, smooth tape handling. my tapes are stored in a climate controlled (cool, dry) environment. I keep my tape path clean.
I'd say that my tapes are sounding better than ever today and I'm now going thru my collection to re-calibrate their relative sound quality in my mind as I've not played tapes much since I made changes in my system a few years ago. they all sound new to me now and I'm really enjoying the journey.
spend time with some high quality tape dubs and they will really pull you in.
there is really nothing like a great tape.
Sunday night I played a very fine 15ips 1/4" master dub of the RCA LSC-2603 Heifetz, Bruch 'Scottish Fantasy' which literally blew me away. I've had this tape about 6 years and had only played it once previously and it had not stood out nearly as dramatically at that time. I don't know it's provenance. but it surpasses the Classic 4-disc 45rpm version quite nicely (and in some places shames it) which I've always liked. it was as enjoyable a listening session as I can remember and I was just so full of joy afterwards.
tape will do that to you.
I only have 150 of these tapes, and i'll likely never have more than 200 of them. vinyl still dominates my listening time. but like a great expensive single malt once in a while it's great to sit back and 'go there'.