wire halyards...

[osteoderm]

A Question: What's the deal with wire halyards?
I've just gotten the mast out of my boat. one of the things i was looking to do was replace the existing wire (rope tailed) halyards with modern rope halyards. Of course, i've found that the masthead sheavebox is far too narrow to accomodate proper rope sheaves.
My options seem to be to either completely re-build the masthead, or put in new wire/rope halyards. Given the complexity of the former (especially given my weird very-tapered, fiberglass(!) mast), i'm thinking of juist refreshing the sheaves aloft and putting in new halyards. It's a dandy excuse to practice up on wire/rope splices anyways...
What is the problem with wire halyards? i can see there being an issue with weight, and with fish-hooks as the wire degrades, and increased chafing on the mast/spreaders, but... If good attention is paid to fair leads, maintenance, and such, what is the big drawback, if any? What am i missing here?