I've since sold my Gilmore Lite and DPS, but I can offer some insight.
I didn't buy my DPS with the Gilmore Lite, and in fact only purchased it about 4 months later, so I had some quality time with the amp and its standard Elpac before upgrading to the DPS. In my opinion the Gilmore Lite is one of the best deals in Headphone amps available, and I was more than satisfied with the sound; rather than buy a new amp, I decided to make the $200 investment into the DPS in hopes of improving what I already thought was great.
My setup at the time was Spitfire DAC (with OPA627) + Supplier DPS, HD 650's, and the Gilmore Lite "stack". The three biggest differences I noticed were bass extension and tightness, overall crispness, and blackness between notes. To be sure, these aren't arbitrary observations that required rediculous attention to detail to even pick up, they were quite obvious - even to my friend who is far from an audiophile. Now to be sure, it didn't turn it into a whole new amp - it made things better than weren't broken in the first place, so if you don't like the sound of your Gilmore Lite, the DPS isn't going to fix your problem.
It is important to note that the power in my NY appartment is extremely poor. I eventually purchased a PS Audio P300 to fix this problem, but that was after I owned the Gilmore Lite. Because of this, I might have been experiencing more benifit out of my DPS than most.
I should also say that I noticed a much bigger difference when I upgraded to a modified Gilmore V2-SE (blackgates and silver wiring), than when I upgraded the power supply on my Gilmore Lite.
In conclusion I would say that the DPS is a valuable upgrade if you are very satisfied with your Gilmore Lite, especially if your power isn't great. At approx. $500, the combo beats out almost anything else in that price range. If you don't like it, it will be easy to sell, people are always looking for GL power supplies.