Alpha slot secondary/tertiary effects
"So Musculature Radial Paragon will make my attacks hit harder, but I will also run faster, get more recovery from stamina, have my web grenade last longer, but gain no def debuff or toHit debuf effect since none of my NRG/Dev power have such a side effect.
Did I get that right?"
Correct, well it'll make you run faster under the assumption you aren't already at the hardcap speed, also under the assumption you are using a power to make you run faster. Since you have swift, that's a yes. It would also effect speed boost, siphon speed (if you're a kin), sprint and super speed. Also correct on the def debuff and tohit debuff.
"Now if I slot Diamagnetic in my Interface Slot for its -toHit effect, will that be enhanced by the tohit debuf enhancement from Musculature? I'm guessing no because the Interface slot cannot be enhanced with enhancements?"
The debuff is it's own separate entity, what I've heard is that supposedly that incarnate powers are supposed to effect each other. I can't confirm or deny that the alpha would effect diamagnetic.
I'll always be a "Champion" at heart. My server away from home.
"When the people fear their government, there is tyranny; when the government fears the people, there is liberty." - Thomas Jefferson

It won't buff diamagnetic.
While this gets into mechanics that aren't necessarily familiar for everyone, Interface works a lot like the "proc" IOs we can get in the inventions system. Whatever effects it grants a chance of, those effects have a fixed, unbuffable (and undebuffable) magnitude when they happen.
For example, most damage IO procs that are, say, 25% chance of 74 damage (at level 50). If you slot more damage enhancement in the attack with that proc, or if you use Build Up, your attack will do more damage on its own, but the proc will still do 74 damage when it goes off.
Interface works like that proc, but in pretty much every damage-dealing power you have. It doesn't automatically affect all your powers, even if they actually do deal damage. It seems that if they can be slotted for damage, it looks like it will add its chance of effect to that power. (In other words, if slotting Musculature Alpha would increase the power's damage, Interface will probably add its "chance of" effect to the power.)
Blue
American Steele: 50 BS/Inv
Nightfall: 50 DDD
Sable Slayer: 50 DM/Rgn
Fortune's Shadow: 50 Dark/Psi
WinterStrike: 47 Ice/Dev
Quantum Well: 43 Inv/EM
Twilit Destiny: 43 MA/DA
Red
Shadowslip: 50 DDC
Final Rest: 50 MA/Rgn
Abyssal Frost: 50 Ice/Dark
Golden Ember: 50 SM/FA
from the wiki: "The Alpha Slot Incarnate Abilities give their aspect enhancement to every power that a character has that can utilize it."
So Musculature Radial Paragon will make my attacks hit harder, but I will also run faster, get more recovery from stamina, have my web grenade last longer, but gain no def debuff or toHit debuf effect since none of my NRG/Dev power have such a side effect.
Did I get that right?
Now if I slot Diamagnetic in my Interface Slot for its -toHit effect, will that be enhanced by the tohit debuf enhancement from Musculature? I'm guessing no because the Interface slot cannot be enhanced with enhancements?