"Vintage" high end gear vs new and upgrade path?

I'm pondering a couple issues that relate to each other.  Let's start with vintage vs new part.   The system is ripped straight from the 90's but was pretty much a Stereophile "A" class setup in its day.  Here it is: 

• Rega P3 with numerous upgrades & Exact 2 cartridge (new)
• Threshold FET10/pc phono preamp,
• Sonic Frontiers SFT-1 => Assemblage D2D-1 ==> SFD-2 Mk3
• Krell KBL preamp (recapped) ==> ML No. 332 amp  (recapped)
• Maggie MGIIIa's (recent factory rebuild)
• Music server (repurposed HP server) w/ Asus Xonar card feeding D2D-1
  

Issue 1:  Have >>analog<< electronics really improved much in the last 25 years?  My sense is that the lower and midrange gear is better, but does that translate to the high end?  This stuff sounds pretty damn good and I'm skeptical that I'd be able to make much improvement without spending vast sums of $$.  What would the weak link be here?

Issue 2:  Despite improvements in digital I'm also skeptical about how much real sonic improvement there has been in high end DACs, especially when it gets beyond 24b/96khz source material (system above is good up to 24/96).  I'm also skeptical about the claimed improvements from DSD over PCM, so I'm ignoring that for the time being.   Obviously connectivity, music servers, the digital audio chain and computer anything has improved greatly and is vastly cheaper than in 1995.  But how far does that actually extend to the sonics?  My sense is not so much.

At the end of the day I'm interested in any upgrade(s) that would create a real, hair-on-the-back-of-your-neck improvement without spending $10k.  But I've convinced myself that so much of what I read about would be only yield an incremental sonic improvement, and maybe even a downgrade.  I need a strategy - which might just be "leave it alone and just enjoy."  Any comments welcome, thanks.