Fifteensquared

Suppose I should have seen the theme coming.  I thought Neo did well to stretch the thematic material as far as he did – even if it may be a little too innuendo-laden for cap-doffing Cavalier tastes.

Across
9 PEA-SOUPER - P[arking] + (as Europe)*.  A word that always conjures up boyhood memories of the film One of Our Dinoasaurs is Missing, although I suspect that it no longer passes muster on the PC front these days.
10 AGATE - a gate.
11 WILLIAM – will + 1A.M.  Highly unusual to see Shakespeare as the definition (albeit by example) rather than as a pointer to an esoteric or vowel-shifted answer.  It does allow a segue into the maritally dramatic sub-theme, though.
12 ENEMIES - (see mine)*. 
13 SKI - ski{n}.
14 THE PENTAGON - t[ime] + (phone agent)*.
17 WALES - w[ide] + ales.
18 GOA - go + A (‘very good’).  Groan; although it must be hard to be original with these three-letter grid-stalwarts.
19/27 ROYAL WEDDING - (L{arge} + dowry gained)*.  The scurrilous anagram here was the highlight of the thematic material, I felt.
21 FORESIGHTED- (horse gifted)*.  Mr Ed meets Mystic Meg, I suppose.
23 MAD - ma + d[ied].
25 LUMP SUM - lumps (as in “lump it or leave it”) + U[nionist] + M.
28 SHREW - hr in sew.
29 NOVELISTS - (L + I[ntl]) in (no vest + ‘s).

Down
1 SPAWNS - pawn in SS.
2 CALL GIRL – (LL + GI) in Carl.  I liked ‘student duo” for LL, but am blissfully unaware as to what makes Carl the epitome of ‘rude’ness.  [Edit: carl is a variant of churl, as in one who is churlish]
3 SOVIETISES – so vie + (is set)*.  Ugly word, but a relatively eye-catching clue in comparison.
4 SPAM - double def’n.
5 IRRELEVANT - I + err< + Levant.
6 KATE - K + ate.
7 TAMING - ta + Ming (“the Merciless” from Flash Gordon).
8 PERSONAL – E.R. son (i.e. “Charles for instance”!) in pal.
15 ENGAGEMENT – double def’n.
16 TARADIDDLE - (RA + did + D[aughter]) in tale.
17 WIFELESS - wireless, with r[ight] for f[requency].
20 YUMMIEST - (mum is yet)*.  Not sure whether this is intended ot be thematically forward-looking?!
22 REMARK - re. + Mark.
24 DIGEST - dig + EST (Electric Shock Therapy).  I wasn’t aware that the latter had its heyday in the ’70s.  Perhaps it was the lesser of many evils at the time – the alternatives being Donny Osmond or watching Scotland in the World Cup finals. [Edit: In fact, EST = Erhard Seminars Training - a less violent, but apparently just as dangerous treatment]
26 SEWN - the four compass poitns.
27 WAVE- W[omen] + {h}ave.  A poetic term for cresting waves.