as someone who has and is currently running 2" full range speakers in dash locations I can say that the spot can sound good, and can result in an excellent sound stage above the dash. Vifa, Peerless, and TangBand all sell decent 2" full range speakers.
note that foam seals between speaker and dash cover/grill are important and should be re-done with foam weatherstripping.
certainly, there are concerns with factory crossover point/impedance.
if you just disconnect them the soundstage will fall apart.