I'm a collector as well, and every now and then I see something very rare. First question I always ask myself - is do I think the rest of the bidders know how rare it is?
If I don't think everyone knows then I'd really focus on the first action. Because once that one's over then everyone will know and I agree that the second one will probably go higher.
You've got plent of time in between auctions to adjust plans. I wouldn't even worry about the second, just place a placeholder snipe so you can reevaluate after the first one.
What's the history of the seller? Do they have a lot of similar items up for bid and is likely to know the value? Or do their items indicate that they might not likely know? This gives you an idea of where the reserve price might be.
Just a few random thoughts