There may be engines which really hate having non engine-parts mucking around in the deck. In the absence of good trashers and in the presence of good virtual money, I'd imagine it could be OK to open something like Baron / Village, if you're going for a crazy double Baron deck that wants to draw the whole deck every turn, or at least draw 1 Village, 2 Barons, and 2 Estates. In this case, each Silver gained may get in the way of the combo, however dubious the combo may be.
For most normal engines that need 5-6 cost parts, it seems good to start with two cards that either gain you money (Silver / terminal + $), trash, or attack, simply because it increases the odds of getting your key 5 and 6 cost parts (like Goons) sooner or disrupts your opponent.