I get GAS attacks too, trust me! I'll see something new I like, do a bunch of research, look into pricing, and then ultimately decide that I should stop looking at it because I don't need it.
Funny thing is, right now I'm as minimalist as they come: I currently have NO basses! LOL. I sold my MIM P because I needed the money, but I still have my Traynor amp (don't look for logic here...I guess I just knew that eventually I would be getting a new bass). So, part of this note was self-instructive in the sense that I want to get ONE bass that will be fulfilling and adequate. I'm not a great player, nor do I have much money, so that shouldn't be a problem
I personally do not agree with your philosophy or what I'd term a "justification" of having just one bass. Being a drumber I've seen a LOT of this discussion in another instrument. How many drums should your kit have? Should you have an array of sonic choices being surrounded by hundreds of percussion items or is "less is more"? Well BOTH are sort of true!
One well-known way to jump-start creativity is to reduce your drumkit down to next to nothing. The smaller the better. What that does is takes away all the myriad sonic choices and FORCES you to concentrate on the NOTES and the MUSIC. The bass-equivalent is one bass that forces your attention on "it's all in the fingers"! It forces your attention onto the notes and the music. It gives you a new perspective and emphasis.
But you also need to understand that it's all about the music and sonic choices are a REALITY. Do they just make shoes in one size? And then tell everyone with big feet to just sort find a pair that is "as versatile as possible"? It's not how it's done.
Basically sonic choices are as much about the music as are the choice of notes, dynamics, etc. I'm sorry but your Fender P or whatever it is, is NOT the same bass as any of my fretless basses. Nor is it like my 8 string (octaves). It doesn't look like my Wishbass, nor sound like my Modulus. And it probably costs way more than my bar basses.
The point is there are basses with quite different characteristics and purposes here! If you have ONE purpose, and only love ONE kind of music and you found the one bass that fits that music. Well, then one bass is exactly right for you...assuming that you intend to stagnate and never learn anything new! I know some players who have played not just the same bass, but the same rig for 25 years, who have an "image" and make a living. I guess it works for them, but I'd be awfully bored doing that. My imagination is always fascinated with new ideas.
Which brings the final point. You have GAS. Why? Probably because like most of us you have an interest in lots of things and would like to learn more. GAS and a new bass is of course easily justified as "educational". The best way to learn about this or that thing (fretless, 6 string, doubled strings, active electronics, etc. etc.) is to actually live with one for a while. Once you've learned about it, THEN things are different. You can say, "this isn't me" and sell it. Or you can say, "I can see lots of places where this would fit into our music". And keep it.
Personally I don't buy the argument that if you aren't playing a bass you have to get rid of it. Wrong question. It isn't ARE you playing that bass, but rather DO YOU EVER EXPECT to be playing that bass sometime in the future. Things that I've "outgrown" or go with music I've outgrown are things I don't "need". But just because currently I'm not doing music that needs 6 strings and not playing my 6 stringers, doesn't mean I'm hurting the poor starving children of India by leaving them in by closet. By selling them I'd be hurting myself, because I'd never know if I could be as lucky TWICE to find another bass later just like them, if I sold them now and then suddenly "needed" them later.