I'm not going to tell you "yes" or "no", because I'm obviously biased. That being said, I'm probably as qualified as anyone to make a judgement based on simple comparison between "test as received"/stock state and "post-surgery" state for these pumps.
The real answer to your question depends on what you want. If you want lots of power, smooth operation, durability/longevity, improved mileage and no smoke, as inexpensively as it can be done... getting Giles to do a performance pump is the answer. If you aren't concerned with smoothness, mileage isn't an issue, and smoke doesn't bother you, then just upping the fuelling will do the job for basically free. It won't be anywhere remotely close to manufacturer specs, your mileage will go down, and you'll be blowing smoke... but it's definitely cheaper.
In all honesty, a question like that is kind of loaded, because it's all subjective - I'd be willing to bet that the overwhelming majority (like 90% and up) of those who are presently rocking a Giles pump will emphatically agree that it was worth the dough. Then again there are guys who have done some of their own mods and swear up and down that they'd never pay that much to have a pump done. A Cadillac and a Kia both get you from Point A to Point B, but there isn't much question as to which is cooler; is it worth the money? Depends totally on where you stand, and what value you place on each characteristic that makes the thing up.
In this case, make sure that you are comparing:
- Improved mileage (We know of people getting 10 and 20% improvements over their "before" setup, but as always, your mileage may vary)
- Better power (25-50% increase in horsepower at the wheels, with nothing but the pump. Good luck achieving that reliably for under a grand any other way)
- Smoother-Than-Stock Operation (Again, not too many mods offer that)
- Durability / Longevity (Giles knows what he's doing, and he tests to make sure. He's has been doing this for longer than I've been alive. Oh, he'll hate me for saying that. :wink: )
- No [Or NextToNo, Depending on your setup] Smoke. (Smoke = Unburned Fuel = Wasted Power and Wasted Fuel. If the environmental considerations are notable in your opinion, that's another point against it. A properly-tuned diesel engine shouldn't smoke, and when Giles does a pump for you and you have properly calibrated and serviced injectors, your machine won't.)
As far as the power gain - yes, you WILL see such a huge difference. I've driven a couple of vehicles before and after pump improvement - you'll notice (and giggle) about the difference. Off the top of my head, I can think of fuelling increases on the order of 100% and at-the-wheels power increases of as much as 44% with no other mods. Will that be the case in your application? Ask Giles, explain what your system is like now, and he'll be able to give you a forecast of what you can actually expect.
Like I said, I won't try to tell you it IS or ISN'T worth doing, because it'd be an obvious conflict of interest. But make sure you're considering all of the relevant data points, otherwise you'll be doing nothing but going on someone's opinion, which may or may not get you to the conclusion you're actually looking for.

Good luck deciding, and let me know if you need any more info from me or Giles.