Re: Herc Fede Swirl
If you love it, then it's worth it, assuming it won't cause you financial distress. I wouldn't try to rationalize why it is or isn't worth it to others.
My personal perspective - I consider Darren, Herc, and Alan all equal masters of different art styles. Sadly, there is just not enough of their work out there, and there is slim to no chance of any more new stuff from the first and last I mentioned. Herc's, we have to be happy with historic creations. With that in mind, if you like it, probably better grab it. Chances will become slimmer and slimmer of finding them, as time passes.
7 string-wise, I have been grabbing everything I can find available, from all three. Price on the one you specified is less that many I have been grabbing.