Marching snares/toms are strange birds. The classics from 50-70 are in more demand over the 80-90 styles. But the classics still won't command high dollar. I've been following the actual selling prices and they can range from $50-$150, depending on the condition and size. 10x14 and 12x15 are usually the standard sizes. It's unfortunate, but these are usually the drums that end up being parted out. In my opinion, it's better to have these sacrificed for parts than regular snares, tom toms or bass drums from a kit.
I see sellers on ebay asking crazy high prices for marching snares. The auctions end and the sellers continuously re-list at the exact same price. Here is one example:
[ame]http://www.ebay.com/itm/VINTAGE-60s-Ludwig-14-11-Marching-Snare-Drum-MINT-CONDITION-/261347457816?pt=US_Drums&hash=item3cd985bb18[/ame]
This is an early 1966 6 lug snare with some minor scuffs. This will never ever sell for $1,000. I feel, with a special buyer, the seller could get at most $200. It's a very nice drum, but the demand/market is just not there.
Sorry for the rant. Now on to your question, "Can anyone give me some insight on the demand level [or lack of] for these?".
The first two Pearl marching snares look to be from the 80's/90's. They are quality drums that were actually made in the USA and are maple shells. Unfortunately, schools or drum corps are not going to buy them. High tension Yamaha, Pearl or Premier are what's in and you can get those used for $250 - $450. So these are setting the price for the "classic" snares. The third Pearl is a high-tension snare from around the 90's. Again, if you listed this snare at $200, someone is going to buy a used, but newer high-tension Pearl for $250, before your snare. :(
The classic snares are a little different. The red snare is not completely original (aftermarket strainer), the white one looks like it's a 12x15 (not an in demand size) and the gold one is missing the badge. The white and gold snares have the Ludwig Classic strainers. If they don't have the snares, new replacements are going to be expensive. All three have the long Ludwig Classic marching lugs, which are not in demand either. All three of these are ideal for people that want to convert them to a more traditional sized snare (i.e. 5.5"x14" or 6.5"x15"), but they will need different lugs (bow tie or mini classic).
When I look for marching drum conversion candidates, having complete, original and re-useable parts is a priority. Wrap condition is not really that important, since re-wrapping is always an option. Plus, there will probably be numerous holes that will need to be plugged after the shell is cut down. After the conversion, a completed snare will never be worth what an original equivalent snare is worth. Converted snares are "player" drums and usually end up having a market value of $150-$200, if sold. For hobbyists that perform conversions, this also sets the market for selling prices. For example, a 10x14 marching snare with bow tie lugs, with bad wrap and missing the strainer is bought for $100. The shell gets cut down to 5.5x14, new wrap is purchased for $25 and a new strainer for $20. It takes a couple hours to clean, convert and re-wrap, so this also sets the market for re-selling a converted drum at the range I listed above.
Sorry for the long winded reply, but hopefully my opinion gives you some insight.
-Tim