I’m sure we’ve all got at least one piece we lust over but can never get ourself to actually purchase, haha.
For me it would be the dope little OP-1. I love what I’ve seen people do with it but with it’s price and limitations I just can’t justify getting one.
Access Virus TI 2
My answer goes in a slightly different direction: I would love to own a real upright bass, but the physical space requirements make it a non-starter. I’ve played bass for 25 years and would love to have access to that sonic palette, but alas, the suckers are big. 
Yamaha CS-80.
Rytm 2. Freezing.
cirklon.
id love one but I just don’t need it 
Dream synths:
Korg PS-3300
VCS3
Actually within reach:
Big effing Eurorack system (for example Make Noise Shared System)
A Neumann U47
Every producer is like “yeah we just mic up our singer with this guy and it always sounds great” and the thing is $9000
I just can’t fathom ever having enough money or desire to buy a $9000 mic… But every awesome studio seems to have one?
Hmm, maybe a microphone collection?
There’s all these interesting concepts and ideas involved with microphones. The fact that a physical thing imparts some kind of character to the sound is really cool. Some work well with percussion, some work well with vocals, etc. Also, it kind of blew my mind that you can do mid/side capture with microphones too.
Hah, these things probably would seem kinda obvious to people coming from a less electronic direction (?) 
But I wouldn’t be getting anywhere with my music, the occasional field recording or some specific sampling is all I ever really get in contact with microphones.
I regret not buying an OP1 when I saw them going for around £600. I can’t justify at the price they are now, which is a shame.
Fairchild 660 or 670
Bode frequency shifter
Emu Audity
Korg PS 3100 or 3300
Con Brio ADS-200
ARP 2500
Kyma (unaffordable)
GenoQs Nemo & GenoQs Octopus (extremely rare & unaffordable)
Cirklon (several reasons)
probably FS1r (rather affordable, but very unlikely suitable for live acts)
Nord Modular (several reasons)
Spectral Audio Neptune (several reasons)
A mellotron. Sounds so awesome but I don’t think I would do it justice. If I would play in a traditional band like I did 20 years ago and not making music by myself as now it would be top of my list.
Genoqs is so dope
Cirklon, Kijimi, Deckard’s Dream, Eventide H9000, Prophet X
One thing I still don’t quite understand is expensive mics. I could understand paying 400-800 for a good condenser or something, but what is it about mics in the thousands / five-figures that makes them so good?
Also, I’d love to own a Moog One someday, or a Buchla. Don’t think that’s happening though.
Deckards Dream, Erica’s Synth Techno System, DSI OB6
I don’t get it either. Surely a $10,000 mic has an equivalent that sounds 99% as good for $1000? Can these guys really hear the difference? I think some dudes just have a lot of money and want boutique stuff just because.
I mean I’m mostly convinced I’ll never buy my own analog mixing console… It’s just easier to use a computer and plug-ins.
I mean people are saying UAD plug-ins sound exactly like the preamps and compressors and EQs they’re modeling. Even me being the poor bedroom musician I am I’m fine with a Waves plugin that gets me almost all the way there. A lot of famous mixers are going 100% ITB now.
API the box
I’ve been in studios with custom Telefunken and Neumann mics that were quite a bit more expensive than the U47. The engineers swore by them.
Obviously as with everything, incremental improvements in character and performance come at a very high cost. That last 1% that pushes a thing over the top is going to have an extraordinary price.