That's reaching. To use the same example, should we say that an increase in elevator travel or elevator area also increases longitudinal stability, because that also would allow a further forward cg position.
Also, increased tail angle of attack won't help if you're near to using the tailplane lift capability, as you'll just be closer to the stall in that case; so even the increase in trim power comes with a caveat; it's certainly not a simple "increased long dihedral = increased stability" situation.
Aside
Just to be clear, we are simplifying things in that the detailed aerodynamics of the tailplane WILL vary with respect to the tailplane incidence angle; factors such as the degree to which is is sealed against the body/fin/bullet will influence the efficiency of the tail, and that saelant may be affected by the incidence (typically, it'll be best sealed at the zero position, given 'normal' geometry).
Also, the strength of the downwash field experienced by the tail is itself a function of the position of the tail; one could argue that the critical position is where the tail LE is relative to the wing, not the tail pivot point; so a change in incidence MIGHT cause a small change in the downwash field; this could easily go either way, depending on the actual configuration geometry, so again no rough-and-ready rule is going to work.