That's the problem isn't it? Diminishing returns. I'm fairly old-skool when it comes to tones, as I have some really nice valve amps and a few simple pedals. The basic guitar into amp tone really comes across in my rig, so I would notice the difference more than someone who was very effects heavy (for example). However, that difference comes at a high price :(
With regard to custom builds, they're just not my thing. I like to see and try before I buy.
After doing some simple calculations this morning, I'd have to lose some nice guitars to buy the Eagle, so it's probably not going to happen. I will have to try one out though, for curiosities sake :)