Maybe have excessive twang, but heck, you have them, might as well try right? I wouldn't spend a bunch of money on hops or liquid yeast for the batch, but maybe an ounce or two and some notty, see what you get.
They are not fresh, obviously, but I see no downside to using them to get your hand back in. A few years is a long time in this game as far as I have seen. Read up on here, use them, but don't expect too much. You will most likely still end up with a drinkable beer
Depends on how you define drinkable. I personally wouldn't want to find out a month later that the beer could have been a lot better. But who knows? I don't think anyone can really say how much worse it will be.
I've used ten year old kits, but I turned them into a stout with new steeping grains, hops. Since everything came out of stock and I pitched on a cake, the total cost was less than $5 plus propane. Turned out fairly well.
The biggest problem is extract darkens as it ages.
Using the old LME cans for starters is a great idea. Since taking a batch of beer from zero to the bottle/keg takes several hours, I'd spend the extra $20 and get fresh ingredients - that way you will want to brew again and again. I have used 6 month old extract in the past and been really disappointed, It was 'drinkable', but compared to batches that use fresh ingredients it wasn't in the same league.
+1 on the starters. i have some 3 year old extract in plastic jugs (which would fare far worse than cans) and have been using it for starters with no ill effects. i ferment out, cold crash and decant the supernatant, though....i still don't want 1.5L of unhopped old extract beer in my new brew!