I would ignore Cnet articles about audio. What that 2007 article said has much right about center channel speakers, and about as much wrong.
You asked two questions. The first was "at what price level will a center channel speaker improve sound?" Let's wait on that for a while because it isn't clear why you have a problem.
Your second question:
Since I am not in the high end market would I be better off upgrading my front speakers and not purchasing a center speaker?
You can answer that right now without spending any money.
Go into your receiver's set up menu, turn off your center channel speaker by telling it you have no center channel speaker. It will redirect that sound to your front left & right speakers. This is sometimes called phantom center channel. Listen while sitting in the middle as well off to each side, and see what you think.
A solution may be as simple as setting the center channel speaker to be a bit louder. Another simple solution would be to move those two chairs a bit (closer together or wider apart, etc.) to see if that improves things.
There was a good
AudioHolics article by Gene that addressed this question of just how good or bad is a sideways MTM speaker used in the center? His answer was they aren't that bad as people say. It does depend on how wide a rooms seating arrangement is, and how far away the seating is. Most rooms aren't wide enough for the problem to become big. Sideways MTM speakers as center channels, in my opinion, get a bum rap.