Finishing Touches solution
by Kegler

The extra letters (shown below in red) spell LITTLE THINGS MEAN A LOT.

Finishing Touches solution grid

Across
1POS(IT)ED
6TEMP + O {place}
11A(PE)X {moist}
12BE(AN)ERY {metals}
13RECITE ("RESITE" hom) {stay}
14PATOIS (TO PISA anag)
15ROOT BEER ("BOOT REAR" spoonerism) {plop}
16YANK (2 defs)
17PASTE (TAPES anag) {heard}
20OLDTIMER (LIED TO MR anag) {tone}
23C(HOPS)UE + Y
26TEMPT (hidden)
30F(L)ED
32ADORABLE ("A DOOR A BULL" hom) {chute}
33GAL + LOP (POL rev) {ruin}
34E + N(C)ODE
35O + TAL(G)IA
36OWLS (SLOW anag)
37NORSE (SNORE anag)
38A(BY)SSES {pints}
Down
1PAR + ToY {dog}
2O + PER + AS (rev)
3SECOND + O {Slower}
4T + AT + TOOS (SOOT rev) {mink}
5DEPEND ("D PENNED" hom)
7ENTRAIN (NINE RAT anag) {one}
8M(E)OWS
9P + R + IN + T {copay}
10OYSTERS (ROY SETS anag)
12BE(B)E
18OC + TA + GON (rev)
19AP + PA(L)LS (SLAP PA rev)
21TY + RAN + NY
22MELLOWS ("MEL + OWES" hom) {Agnes}
24U + TO + PIA {palace}
25NEED + LE {kilt}
27ERA + TO {mouse}
28MO(L)AR (ROAM anag)
29AREnA
31DRESS (rev hidden) {Marty}