Have you sold your traditional instruments to switch to Pianoteq?

Moving this topic from the Organteq forum to the Pianoteq forum where it was likely intended.

I am reminded of Michael Price's advice on when is gear worth a significantly higher price tag than a plug-in or a similar low-end piece of gear: "when that difference inspires you."

So, does your old gear "inspire you" as you compose?  If so, keep it, you can't replace that ephemeral aspect to it.  My guess is that you're more likely to regret it/miss it than feel comfortable about liquidating it to cash as the cash isn't the value of the gear, the value of the gear is what the gear does to help you create.  If you truly never use the equipment or it doesn't inspire you, then that's a totally different story...  I fight with limited storage space all the time, but I never regret better utilizing any of the gear I have (or the space that I work in to accommodate it).

You can try to live/work without the gear for another month or more and see if you being to miss it more or less, but since you're already thinking you'll regret ditching it--and asking others if you're thinking is correct, you're instinct is probably a lot more accurate than any advice we could randomly give you.  You could also try ditching PTQ for a period of time and exclusively work with the vintage gear and see if/how your workflow changes.