1) I would never go out on a limb and purchase new anything.
2) The used market has gone completely off the rails
3) A well tuned V-8 full sized square body truck can routinely get 18+ miles per gallon, for my driving needs, I'll stick with the old stuff I understand.
i was just thinking about that the other day: i may switch back to v-8 sbc for the following reasons:
1) It's simpler/easier/faster; You have almost an endless supply of heads/intakes/cams/whatever you need. The aftermarket for SBC is unmatched by any engine. The v-6, including buick, really don't have much. Even with the short popularity of the Grand National, the v-6 never took off in popularity and probably never will.
2) The weight advantage of the v-6 is not that great. All things being equal (both engines using iron heads) it's about 575lbs for the 8 vs. 425lbs for the 6, so about 125 lbs. However, IF you go with aluminum heads/intake on the sbc, and with sbc it's really not difficult or expensive, now we are talking about 90-100lbs difference. 90-100lbs. is really not much for an engine AND considering how much more power the v-8's have, you are gaining much more in power than losing in weight disadvantage.
2a) Engine setback: i thought this was a big one BUT now i don't think it's that great either. On the truck, the front of the v-6's block (not the accessories) IS behind the front axle centerline by about 1". A 4.3 v-6 is roughly 4 1/2" shorter than a v-8. However, not all of the 90-100lbs weight difference is in that first 4 1/2 inches. So, here, i SUSPECT the engine setback is not as HUGE a difference as i once thought.
Does ANY engine setback help performance? Probably. i'm not autocrossing, so to me it doesn't make much a difference.
3) Size advantage. SBC's practically fit into almost anything. One of the big reasons why i went with the 4.3 is so i could do this:

Yes, it can be done----if you cut down on the rich desserts.......

i could practically rent this space out on AirB+B.....
This HAS made it so much easier to work on the engine. But with a TopSide creeper, this would be unnecessary.
4) Performance/versatility:
The v-8 just hands down blows away the 4.3. power-wise. Even a stock basic crate 350 makes more power without trying and with no add ons----nitrous etc. You can easily build or buy a new, running 383 delivered to your door in a few days. Thats an easy 340-420 hp N/A.
5) MPG advantage. i'm generally finding lose 2 cylinders, gain 2 mpg. That's significant. But if you don't do that much driving and i don't, then how much are you saving?
Overall verdict: Even with all the small advantages here and there of the 4.3, the v-8 still overall wins out due to versatility, cost and ease of operation/build out ability.
i picked the engine because i like it and wanted something physically smaller. It's funny that i'm on GM's case for dropping the v-6, and here i am considering the same. i still really like the engine though.
It's kind of the same thing with manual transmissions. i've always been an automatic person, never wanting a manual in any of my cars. But i feel it should still be offered because a lot of truck people and enthusiast types (corvette, camaro etc.) still want them. Plus, they are simpler and i feel that there are always advantages to that.
From a sales standpoint, if the demand is really that low, then i guess it makes sense to drop it?