Another alternative I have been considering is replacing the to hit bonus ONLY with:
Level +3
This would replace the following:
* Stat mod
* Enhancement
* 1/2 level
Looking at your proposal, I assume this level+3 modifier is meant to replace a player character's primary attack mode in combat (ie. INT for wizards, STR for fighters/rangers/paladins, WIS for clerics/druids, etc ...)? For example, this proposal would seem a bit odd for a wizard with an 8 or 10 strength, doing a STR attack with a staff or weapon they are not proficient at.
The question is whether the equation:
[level/2] + stat mod + enhancement = level + 3
or stat mod + enhancement = level - [level/2] + 3 (*)
(where [level/2] is level/2 rounded down)
makes sense for the levels of interest.
As an example, minmaxers like to have 18 or 20 in their primary stat, which would give a respective +4 or +5 stat mod. Taking 18 for the primary stat, equation (*) becomes:
1 + enhancement = level - [level/2]
Solving this equation for various levels:
level 1, enhancement = 0
level 2, enhancement = 0
level 3, enhancement = +1
level 4, enhancement = +1
level 5, enhancement = +2
level 6, enhancement = +2
level 7, enhancement = +3
At level 8, the mixmaxer would have already added +2 to their primary stat, which changes the equation (*) to
2 + enhancement = level - [level/2]
Continuing on, we get:
level 8, enhancement = +2
level 9, enhancement = +3
level 10, enhancement = +3
level 11, enhancement = +4
level 12, enhancement = +4
level 13, enhancement = +5
At level 14, the minmaxer would have another +2 added to their primary stat, which changes the equation (*) to
3 + enhancement = level - [level/2]
Continuing on, we get:
level 14, enhancement = +4
level 15, enhancement = +5
level 16, enhancement = +5
level 17, enhancement = +6
level 18, enhancement = +6
level 19, enhancement = +7
level 20, enhancement = +7
At level 21, the minmaxer would have another +2 added to their primary stat, which changes the equation (*) to
4 + enhancement = level - [level/2]
Continuing on, we get:
level 21, enhancement = +7
level 22, enhancement = +7
level 23, enhancement = +8
level 24, enhancement = +8
level 25, enhancement = +9
level 26, enhancement = +9
level 27, enhancement = +10
At level 28, the minmaxer would have another +2 added to their primary stat, which changes the equation (*) to
5 + enhancement = level - [level/2]
Continuing on, we get:
level 28, enhancement = +9
level 29, enhancement = +10
level 30, enhancement = +10
One can compare this to the expected enhancement bonuses on page 225 of the 4E PHB:
level 1-5, enhancement = +1
level 6-10, enhancement = +2
level 11-15, enhancement = +3
level 16-20, enhancement = +4
level 21-25, enhancement = +5
level 26-30, enhancement = +6
This level+3 to-hit bonus proposal appears to overshoot somewhat in the paragon and epic tiers, and slightly nerfed at levels 1 and 2.
From my experiences with playing at paragon and epic tiers, I got the impression that combat took longer in general at higher levels even when equipped with appropriate level magic weapons.