I feel like encounter levels should be kept vanilla - the same level for easy ones, 2-3 lvls higher for tougher ones. Especially at early levels, I found that same-level encounters don't even necessary need for healers to burn their encounter heals.
I guess this is a case of "different strokes for different folks", but I couldn't disagree more.
The base assumption in 4e is 4 PCs. Everything in the game is geared to support and interact within this assumption. When you have less PCs the party is gimped. If you have 2 PCs, as an example, they have half of the assumed actions in a round - be they attacks, moves or recovery. Missing on attacks becomes even more mathematically significant with less players. I'll use levels 1-3, IMO the most vulnerable levels, to illustrate.
The base XP budget for 1st level is 400 XP, which would equal, as a baseline, 4 standard 1st level monsters, or up to 16 minions. These can be exchanged for 2 elites or 1 Solo. At first level you cannot use LEVEL-anything monsters because they do not exist. XP budget for 2nd level is 500 - 5 standard 1st level monsters or up to 20 minions. XP budget for 3rd level is 600 - 6 standard 1st level monsters of up to 24 minions. You can also replace these for elites and solos based on XP budget.
Based on these numbers you start to see the disadvantage of keeping encounter levels "vanilla" when you have small parties. At first level budget your action economy would be at a ratio of 1:2 for standard or 1:8 for minions, only being at 1:1 if you use elites. At second level budget the action economy worsens to 1:2.5, 1:10, and still possibly 1:1 only for elites. Third Level budget 1:6, 1:12 or 1:1.5 if elites.
Detractors of 4e used to say that it was impossible to kill PCs in 4e. From levels 1-5, I have TPKd more PC parties in 4e than all other editions combined.
If you mean keeping LEVELs vanilla, but are decreasing XP budgets to match, then you are pretty much doing what I'm advocating but from a different angle.
2 player XP budgets become:
As for changing Second Wind mechanics - your proposed rules would make Dwarves almost obsolete in that regard, since that is considered an ability special just to them as of PHB1
You are right in assuming it would take away the specialness of dwarves. You can simply make the dwarves racial ability a free action instead of a minor. Same effect, same balance.
All of these are some of the examples that showcase how powerful 4e can be in the hands of an experienced DM that works within the framework. The game is extremely malleable.