Dogman,
I can't help you much with tonal comparisons... I have a '74 D-25M with spruce top and arched laminated mahognay back. It's a cannon... rich dark tone with incredible projection and sustain. I love it in DADGAD. I did play an all 'hog flat-backed D-25 some 37 years ago, and chose my D-35 instead. But that's too long ago for me to compare its tone to my '74... I have heard that the flat-backed all 'hog models are a little more understated and "woodier" in their tone... but I don't have a good idea what that means.
However, here's a bit of D-25 history (from Hans Moust's book), so you can see what is out there:
The D-25 was introduced in 1968 as Guild's "budget" dread. It was essentially an all solid mahogany (T/B/S) version of the D-35, and had the typical flat/braced back. In its first year, it had a black headstock overlay with inlaid Guild logo and smaller pickguard. That was changed to a plain headstock with silk-screened Guild logo and standard pickguard in '69.
D-25s with spruce tops and laminated, arched backs were introduced ~1974 (my '74 is spruce topped/arched back). However, during the transition period there also were D-25s made with mahogany tops and laminated, arched mahogany backs. So, during this brief period from '73-'74, you can actually find three versions of the D-25:
(1) All mahogany with (solid) flat backs (1968~1973);
(2) Mahogany topped with arched laminated mahogany backs (sides are solid mahogany) (1973~1974); and
(3) Spruce topped with arched laminated mahogany backs (sides are solid mahogany) (~1974 on).
From watching eBay over the last 4 years, the spruce-topped D-25s (#3 above) from the mid-late-'70s are the most common (as might be expected, they were made for a longer period). You do have to look carefully at these on eBay... some sellers think that the M in the model designation (as in D-25M) means it's all mahogany. It doesn't... the "M" refers to the stained top finish (usually on a spruce top). During the '70s they also come in "cherry" finish (and brown?)... and later in a variety of finishes (natural top = NT, black, burst, others?)
The all solid mahogany flat-backed version (#1 above) shows up reasonably often (maybe 10-12 a year). These are easy to spot... they will typically have SNs dating to '73 or earlier, and have back bracing visible thru the soundhole. There are/were a couple up on eBay this past week.
The arched back mahogany topped D-25s (#2 above) are the rarest of the three on eBay...I have seen maybe a couple a year over four years. You have to look a bit carefully to ID them... they will typically have SNs dating to '73-74, and the top will show the more prominant grain of mahogany (compared to the stained spruce tops, which often exhibit very little visible grain or figuring; and, of course, they will have arched backs with no back bracing visible thru the soundhole).
I can't say I have seen any real price differnetial between the three on eBay... all tend to sell in the $500-$750 range, depending on condition and the vagaries of the marketplace. I would say anything under $600 is a good deal... under $500 a steal. But, it's all relative...
Good hunting!
Dave
