The issue of elevons vs separate elevators and ailerons has been flogged to death several times in this forum.

Pros for elevons are "simplicity" and weight (marginal).
Cons are guaranteed loss of aircraft if either servo or linkage fails.

Split control surfaces cost you the additional weight of 2 more servos (and associated linkages), but give you (with the appropriate mixing on your computer radio), dual redundancy in both pitch and roll.

My advice is go with split control surfaces.

As far as the new inlets go, buy them. JHH did a beautiful job with the new, area-ruled, inlets and your Mirage will will definitely display improved performance with those inlets.

Good luck,
Peter