I never had a problem with adventuring day in 4th edition, it could sometimes be only 1 encounter, sometimes 3. I balance the encounters difficulty accordingly. If it’s gonna be just 1 encounter, it’s gonna be a really hard one that still push the players; if it’s 3 encounters, I’ll make them a little easier (but still hard so that the players feel challenged).
One thing to keep in mind is, like previously said, every classes used the same power distribution (at-will, encounters, daily, utility), so there is not some class that are ‘better’ when there is fewer encounter or when there’s a lot of encounters. They all have exactly the same ressources, so there is no problem of one class feeling cheated if there is only one encounter and vice-versa.
Also, combat are extremely well balanced, so it’s easy for the DM to build an encounter that will be very challenging even if there is only one encounter, so you don’t feel forced to have to make multiple encounter in one day to challenge your players.
Finally, even if your players still have a lot of healing surge, healing during combat is still limited. Each player can do one Second Wind action that will allow them to heal a quarter HP. Leader class that can give heal via their basic encounter power are limited in their use per combat (only two use of healing word at heroic tier that will heal a quarter +bonus). Then there is a couple of powersthat can also allows you to, but the thing is, regardless of if you do 1 or 4 encounter per day, you won’t have more healing per encounter if you fight less. Think of it as if most of your power reset after each combat (except for the dailies) so you start every fresh.
