I agree that you should consider their mana development but most importantly IMHO you should consider also your own mana development and balance it all.
- If they play ancient tomb and pass, i would seriously consider wasting the tomb as it is clear hint that their opening hand contains high casting cost cards. In that scenario, wasting put them behind farther than me (even more if i have a mox too).
- If they play ancient tomb + a cc2 card (whatever), wasting the tomb would be making a bet you are most probably going to loose. I agree that hitting a critical land with the good timing could be a winning play but i think the timing is not good here. If you are against MUD, the most probable is that they have 2-3 mana cards in their opening hand. They would never have kept a hand with only an ancient tomb and since MUD are playing nowadays with quite a low curve, it is most probable that wasting the tomb won't prevent them to play their threat next turn. More over, what is your position after you waste them : exactly the same as before the turn 1 with one less land in hand (and them too) but they have something on the field (you lost tempo). As you are playing against a mana denial deck, you might really need that land later and your mentor will hit the field one turn later than it may have (if it ever). Basically, you slow them down a little but you slow yourself much more.
To make it short, i think that on the draw you should first build your mana base before trying to hit his own. When you waste his tomb, you may expect that you got yourself one more draw before the heavy threats are coming down. But what are the probability that you draw what you need (even with brainstorm, ponder, ...) ? I am not sure it is worth the cost (i.e the loss in tempo).