I like a pickguard, myself, but my only experience has been with flamenco guitars. They have scratch plates on the top and bottom, as they get subjected to all kinds of abuse. Many players fashion them out of shirt boxes (!) — my old Condé Hermanos has one of these, installed by the original owner — and glue them on so that they're practically invisible. Nearly fourty five years on, and the guitar is in remarkably good shape considering the amount of wear it's had. I think that the mojo of a well-maintained old acoustic is greater than that of a prematurely beaten-up one that has had to be consigned to the scrap heap.

I use the pickguard.

Interesting info about Willie's 'Trigger' from wiki :

"Nelson's principal guitar is a Martin N-20 nylon-string acoustic, which he has named "Trigger", after Roy Rogers' horse. Constant strumming (with a guitar pick) over the decades has worn a large sweeping hole into the guitar's body near the sound hole (there is no pick-guard on the Martin N-20 since classical guitars are meant to be played fingerstyle instead of with flat-picks). Willie once commmented it was caused by a little too much Whiskey River. Its soundboard has been signed over the years by over a hundred of Nelson's friends and associates, from fellow musicians to lawyers and football coaches. Nelson has often said that when the hole in Trigger's body makes the guitar unplayable he will retire."

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Being able to play and enjoy music is a gift that's often taken for granted.

Don't leave home without it!

I don't think that a smaller pickguard would have all that much adverse effect on tone or volume but having said that the enormous pickguards on Everly Bros. Gibsons were referred to as the Tone Killers.

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'65 Strat,65 Mustang,65 Jaguar,4 more Strats,3 vintage Vox guitars,5 Vox amps,'69 Bassman with a '68 2-15 Bassman cab,36 guitars total-15asst'd amps total,2 vintage '60s Hammond organs & a myriad of effects-with a few rare vintage ones.

I use them on my acoustics just because i strum hard and don't really care for big ugly scratches in my guitars.