Jeremy Clarkson is weighing in on the whole, "restore vs. resto-mod" debate. Me? I tend to value originality, and the market my cars play in does too. That said, I also think modifications which materially improve the car while also being true to its nature are also to be admired. Putting a Chevy 350 V-8 in a Jaguar XJS sedan I think is a pretty horrible thing to do, but putting a monster Alfa V6 in a tiny Alfa sports car (and, if you follow that thread, f-all else to it) is fine. Doing things to fix things that were actual mistakes in the original engineering, like the fixes on the E-type Jeremy mentions, are more than fine as well.
But, ultimately, I've come around to the opinion that, "it's your car, do what you want to it." I admire any modification when it's done well, and I laugh uproariously at any that are done poorly. Take care of it, and don't half-ass anything.