I think they will continue dropping.
1. Historically, second-tier Lambos have profound depreciation. Jalpas typically run $20k to 40k.*
There's a few down near the $40K area, but most models still push $50K plus due to rarity. A $20K Jalpa is the equivalent of a $20K Maserati GT. Far from the norm of an example you'd actually buy.
2. There are a lot of Gallardos. Production numbers are very high. Half of Lamborghinis ever built are Gallardos (around 15,000 of them are running around)
Except the car has been updated 3 times over the course of 10 years, which devalues the previous model as owners start to trade in. I already posted what 2004 examples are going for with high mileage; $90K and leveling. The Huracan will not push that value down any further after 10 years, it will affect the 3rd facelift that was incorporated & drive them down a bit to the LP560-4 levels.
3. The argument could be made that the Gallardo was a lot better than the Jalpa and that despite it's high production numbers it's still a Lamborghini and therefore any further depreciation is unlikely. That hasn't stopped the quite universally loved Ferrari F355 from approaching the 40-60k range.
The F355 pushed down because of the 360 Modena, which has been pushed down due to F430, in turn thanks to the 458. F355 values aren't going to dip anymore & 360s likely will not either by this point.
The Gallardo wasn't universally loved. There is more than 3 times as many Gallardos as F355s.
Not even close. 13,992 Gallardos. 11,206 355 models: 4,915 355 Berlinettas, 2,577 355 GTSs and 3,714 355 Spiders.
Ferrari, historically, is a higher valued marque than Lamborghini, and that is quite clearly shown in auctions. The Huracan will be the next hot new thing, and I think it will make the Gallardo quite old news when it comes out. Lamborghinis are as much about the look (whats new and hot) as they are about performance. You wouldn't by an 8 year old Lamborghini if you want to look hot.
The problem with this idea is that the 2004 Gallardo was old news when the LP560-4 came out, even more so when the 2nd facelift came. The other issue is this attempt to compare the F355. Ferrari has built 2 generations of its MR V8 supercar in the same time frame Lamborghini usually builds one model. Comparing production numbers won't mean anything when you compare the actual amount of cars Ferrari produced for 2 generations in the same production time as the Gallardo:
Gallardo 2004-2014 - 13,992
F430 2005-2009 - 12,000 units including Scuds & 16M.
458 2009-2014 - 2,400 to the US alone (according to Ferrari of Denver that the US is allocated 600 a year). 2012 saw at least 4,350 examples produced.
Ferrari values fall because of the short time frame they push out the next model. You can't compare the Gallardo to the F355 either due to the era & amount of time between them that will affect said value; 5-11 years worth of time.
All of this is to say that I think Gallardos will continue to depreciate a little bit more. Perhaps not down into the 40k range, but maybe $10-$15,000 more. The ones posted above are all relatively low mileage. And while supercar mileage works differently, there is a lot of Audi in the Gallardo...
Those are not low mileage for a Gallardo; it's the equivalent of a C6 Corvette running 150,000 miles. And considering that 40,000 mile Gallardos are not very common, it should give an easy idea as to where the market for the Gallardo is still currently at; $110,000-$120,000+ for a decent example of the '04-'08 generation.