IMO, we often tend to get too wrapped up in how much we've already spent for something and what we could sell it for (happens to me all the time) but maybe we are missing the point. As a general rule, especially for modern trains, the collectabilty ship left port long ago and sank in the bay, so why worry about it? To me, the relevant questions are:
If I like the engine, can I enjoy running it in conventional mode? Lots of people do this.
If I can't enjoy running it in conventional, can I buy a similar PS2 or PS3 engine? Maybe swap shells and sell the extra bits? (I've seen WTB posts for PS1 boards.)
If neither of those options is a possibility and I have a sentimental attachment to the engine, I'll swallow hard and pay for the upgrade. If that brings pleasure, the extra couple hundred bucks will be long forgotten.
My 2 cents.
