Questions about Preamp Tubes

I've had my Mapletree Audio 2A/SE for > 2 years and no tube issues yet. It is by far the cheapest piece in my system at only $675, but the sound is glorious IMO. If you rank gear by price I guess it is "lower-end", though certainly not by sound.

The only problem with tubes is you might get the bug and try different types of tubes to play with the sound. I now have 5 sets of 12ax7/cv4004 and 4 sets of 12au7/5814a tubes and having a blast :)

"Tubes in preamps normally last 5000 to 10000 hours of playing time"

It makes sense to me that tubes in a pre-amp would have greater reliability than in power amps.

But is it all or nothing? In other words does the system sound the same for this long and suddenly die?

Or do subtle changes for better or for worse occur in the sound as the tubes age?

My guess would be the latter, but I do not know for certain.

Some high end tube vendors like VAC even offer automated health monitoring systems in their products to address this. IS this a frivolous feature that does not add value or the real thing? I suspect the latter.

The first case would not concern me much. The second would, in particular if many tubes are involved. I want to spend my time listening, not having to constantly check tube health if I think something does not sound right.

After the initial breaking in period (of the preamp), the sound will be fine for 5000 - 10000 hours of playing.
When the tubes are nearing the end of their life, you will hear them fade away (more noise).
Replacing them after a few years won't cost you a fortune.

15 years ago I owned a Audio Research LS-2b preamp (only one tube inside). The tube did survive the upgrade to a LS22, 3 years later.....

"My understanding is that it becomes very, very hard to differentiate between tube/SS in high-end products; however, is this the case in lower-end models?"

This is a very good question. I think you are on to something here.

I've noticed that the better tube systems I've heard that cost upwards of $10000 do not sound all that much different from some SS products that may cost 1/4 as much. SS products from Musical Fidelity, Classe, and Krell I've heard come to mind.

Even the late 80's vintage Carver SS pre in my system that provides a tube emulation voiced output is not too far off from what I've heard.

Any thoughts on this?