Looking at this in the short- as well as the long-term, I'd have to agree that the law of supply and demand really dictates a lot of what one might be able to get for an instrument.
Earlier in the present recession (probably about 3-4 years ago), there was a period of about 6-12 months during which there were a relatively large number of Alembic instruments up for sale nationally on Ebay, GBase, and Craigslist. They included everything from Series II bases to Epics. Most listings included some type of statement alluding to the need for the sale being loss of job. Prices were quite reasonable (I picked up an 86' walnut Distillate in just about perfect condition for $1,800.
Recent months have seen fewer Alembics offered for sale overall (is this a good indication that we are in recovery) and the majority of those that have been on the market have been Epics. For those smaller number of non-Epic basses available prices have risen accordingly with sellers asking $2,300 to $3,500 for Spoilers.
As far as new basses go, it's like buying a new car, as soon as you drive it off the lot it depreciates significantly. So, buying used would appear to make the best sense and I applaud those who have waited for years for just the right bass to come up for sale. Personally, I swore I would never buy new BUT...I looked for over 2-years for a Further guitar for my son and eventually had a build done because nothing came up for sale while I was looking (over course several popped up as soon as I made the down payment). I then finally came to terms with the fact that what I was looking for in a bass for myself would be very unlikely to appear and currently have a Signature build in the process (Yes, I'll admit that I was also a bit jealous of my son).
As far a new builds go, I think one thing that has a tremendous impact on how much of your original investment you get back is the extent to which the instrument is customized. We all have things that we convince ourselves that we just need (as opposed to prefer/want) to have on our new basses. These aspects of the build, including LEDS, inlays, cutaways, high priced front and back lams can get to be quite expensive and may add thousands of dollars to a build. Based on personal experience I can say that these are extremely hard to resist. The problem is that if I ever resell at some point, others may not have nearly the need that I did to have front and back lams, continuous wood back plates, premium woods, LEDS etc. making it a lot more difficult for me to get even close to what I paid for the instrument.