Not a dumb question ...

No reason at all not to try No Shine on the back and sides. I did this on my lace pieces, with glue at the front.

The reasons are as you suggest -- no shine is a bit weaker than blue liner, but less detectable (true for me, and is the general consensus). Any worry over shine on the back and sides would depend on your density. I wear a very light density, so even Walker's would shine a bit, but it was strong enough for me in most situations, though less so than blue liner (de/re weekly).

Walker's also has fewer clean up headaches than blue liner.

~FB