In fact, Texas, when it joined the union, reserved the right to, at any future date, break up into five states for this exact purpose. It would increase our representation in the Senate from two to ten.
Except no it wouldn't, unless you think those five separate states would forever after vote in lockstep with each other instead of going their own way and looking out for their own interests. Sure, those interests would be similar because they're in the same geographic area, but that in no way guarantees political cooperation on all important issues.
And while, as a whole, they may get stronger in the Senate, they'd individually get weaker in the House.
Since representation in the House is based on population, they would not get weaker in the House. The population wouldn't change. The population distribution wouldn't change either. Representation in the House would remain essentially the same. There may be some slight realignment depending on where the state were divided, but total representation would remain pretty much the same.
Hence why I said individually... each state would represent 20% of the state population, on average.
Since representatives in the house are elected by geographic districts, assuming for the moment that the state were divided along those same lines so that no district were split, the representation in the house would remain identical to what it is now. Assuming that some of these districts did get split when the state divided, then yeah, some of the represenation would change. But again, only slightly.
So in other words, my Senator would now represent the (on average) 20% of the state that I live in instead of representing the 100% that s/he represents now, (in theory) better representing my views. But my Representative in the House would pretty much be the same -- based on population and based on my district as it is now.
But yeah, this is all just academic as it probably won't ever happen. My original point was that when you combine or eliminate states (as was being discussed upthread) you are actually advocating for less representation in the Senate.