I'm trying to understand how exactly Strength effects the powers in Might. With the cap being easier to reach, is there any reason to stack strength after that or is there something I'm missing?

Strength gives a damage boost for melee (the cap you mentioned)
Strength super stated gives another special damage boost on top of the melee boost.
Strength improves knockback and knockback resistance.
Strength improves tangible hold break free
Strength lets you lift larger objects that can be thrown for endurance free AOE damage.
Strength increases the resistance you get from invulnerability if you're willing to dabble in the power armor set.

Ok, this is what I was looking for. I'm trying to figure out if this is worth going for if I'm at the cap or should I focus on a 3rd stat like End maybe?

The Enrage ability scales with strength also.

Realistically you'll need both as the higher damaging powers in might (haymaker) require a good amount of endurance to fully utilize. I know that there are only 2 "super" stats but you should really try to focus on 3 to 4 stats through the combined use of your super stats, talents and equipment.

There are only three reasons to stack STR beyond the supposed +20% melee damage cap for a Might character, and really only one if you're looking at the powerset in isolation:

1. If you took STR as a superstat, then obviously you need as much of it as you can reasonably acquire to boost your superstat damage bonus.

2. If you took and regularly use Enrage. The damage bonus from Enrage scales with STR.

3. If you took Invulnerability (which isn't a Might power, but it fits thematically with Might, and stacks better than Defiance with Defensive Combo). Invulnerability's static damage absorption, which is probably the most important aspect of Invulnerability for the bulk of solo content (henchmen, principally), scales with STR.

Otherwise, you have incidental reasons to take STR, like the ability to lift things (which isn't very important from a game-mechanics' standpoint, but it is thematically appropriate for a Might character), or knockback/tangible hold resistance, or knockback strength -- but nothing that has much to do with the nuts-and-bolts functionality of the Might framework in specific.

Personally, I went with STR + CON as my superstats, with END as my third priority on equipment. You definitely want to have a decent amount of END, because the only effective bottleneck that determines whether or not you can use a power is your maximum energy value. Recovery and Intelligence both help in their own ways, but the former won't make a 300-energy power castable if you have 100 energy, and while Intelligence basically increases your energy total in a different way (by making powers cheaper) it doesn't increase your energy generation capabilities any (as END does, indirectly, because energy builders return a percentage of the total).

END is one of the few stats which offers a static benefit as you level; in other words, your energy pool always corresponds to 100 + your END stat. END will not allow you to start fights with high-energy-cost powers, but it's pretty easy to build up enough energy within the first few seconds of a fight.

At some point, you may feel like you have enough END, in which case it'll be time to branch out further. Only you can determine that, through playing and growing accustomed to your build. Some builds will have more energy-intensive powers than others. As a general rule, though, I like to make sure I have enough energy in Defensive mode to fully charge the most expensive power in my build. After that, a larger energy pool is just gravy, IMO -- but then again my build gains energy faster than I can spend it, in most fights, so it's not a big deal to drain my bar in one shot.

There is some debate now as to whether superstating STR is worth it, now that most any melee build can theoretically acquire the full melee-only damage bonus from STR through items alone. Purely from a numerical perspective, it probably isn't worth it, but I can't imagine rolling a Might concept which couldn't pick up a truck, or knock things half a mile away with a punch, or resist knockbacks very well.

Also, as far as I know, the exact amount of STR you need to hit the melee-damage-bonus cap is as yet unknown, and getting the perfect mix of stats from items is easier to talk about than actually to do. By taking a different superstat, you're likely spreading your stat bonuses from items thinner than they might otherwise be.

Unless you wanted to go CON/END, with STR as a third priority. Then you'd have basically the same stat spread I do now, with the caveat that your benefit from STR will vary as you level, whereas my benefit from END can only, at worst, remain the same as I progress.

On a semi-related sidenote: We can debate the merits of STR or END as a superstat on a Might build, but I'd really seriously never consider dropping CON. Whether you want to play a so-called tank or not, melee characters will tend to take more hits than their ranged counterparts, and so extra hitpoints are always good. Plus, Defiance and Invulnerability both scale with CON.

DEX/EGO is an option for maximum DPS, but I wouldn't do that unless I got some sort of side benefit from my power selection for either or both of those. LIke, say, if you wanted Lightning Reflexes. Haymaker with a full-crit build is surely a sight to behold, but I think at the end of the day working out all of your equipment priorities on such a build would be more trouble than it's worth.

Your mileage may vary. The only hard-and-fast rule is that you can't have it all.

Which is one of the most fun parts of the game. I'm starting to throw trucks and troop transports now. YAY!