Ask anybody who has ever been in a gun fight if they would have liked less ammo in their gun.
Okay, how many folks here have been in an actual gunfight? Show of hands.
Now, how many of you actually anticipate being in an actual, guns-a-blazin' gunfight at some point in your life?
Last but not least, imagine that you're famished right now, like you haven't eaten at all today, (bonus points if you actually are that hungry right now) then tell me what sounds better right now...A single hamburger or a bacon double cheeseburger?
The point is, wanting more ammunition in a gunfight is like wanting more food when you're extremely hungry, you may want it, you might even think that you need it, but factually speaking, how many folks have actually run out of ammo in a gunfight, and if they had it on them, would it have made a difference, would they have been able to make use of it?
FACT: If you're outgunned, then you're at a disadvantage which cannot be overcome simply by carrying more ammunition. In other words, if you are facing multiple assailants, then having a gun that holds more rounds and/or carrying more magazines/speedloaders isn't going to even the odds, not by a longshot.
Don't get me wrong, there's definitely an advantage to carrying firearms which hold more rounds as well as spare ammo, because obviously they enable you to potentially stay in the fight longer, but that doesn't mean that you'll necessarily need that many rounds, much less be capable of effectively making use of all of them.
In cold weather, I myself carry a double-stack SW40VE, but in warmer weather I carry a Shield 1.0 because it's easier to carry, and I have no intention to "upgrade" to a Shield PLUS when the added thickness as well as the added weight of a fully-loaded magazine would make it less comfortable to carry in Summer, yet make no difference in Winter. As previously stated, I'd sooner update my existing Shield with aftermarket magazine extensions than buy a new Shield PLUS.