Solution to 8D has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
ACROSS
1 Competence at organising foyer picnic (11) PROFICIENCY*
9 Secrecy about road’s condition? Not at first (7) STEALTH {ST}{hEALTH}
10 On regular roof, statue is well-built (6) ROBUST {RoOf}{BUST}
11 Measuring instrument looks the same from both ends (5) RADAR <=>
12 Squeeze half of them with steel (7) EMBRACE {thEM}{BRACE}
15 Roman emperor starts new era ruling obscenely (4) NERO Acrostic
16 In a riot, await flyer, spend wastefully (6,4) TRIFLE AWAY*
18 Being understanding towards them? Useless! (10) EMPATHETIC {'EM}{PATHETIC}
20 At deli, cook is not working (4) IDLE*
23 Copy-cats or birds? (7) PARROTS [DD]
26 King, new, Conservative, leaves for German capital (6) REGENT RE(-c+g)ENT
27 Headgear for democrat leader surrounded by fruit (7) BANDANA {BAN{De...t}ANA}
28 Thoughtful desecration? Ridiculous! (11) CONSIDERATE*
DOWN
2 Monarchs’ measuring devices (6) RULERS [DD]
3 Alpine wind on flowerless plant, we hear (4) FOHN (~fern)
4 Confirm fun making sweet bread? (4,6) CORN MUFFIN*
6 Funds to frighten money-spinner (4,3) CASH COW {CASH}{COW}
7 Alienated eccentric caught in regular eddy (9) ESTRANGED {Ed{STRANGE}Dy}
8 Fixer to stray, lose way even (6) ?E?D?R (Addendum - MENDER MEaNDER - See comments)
13 Adjusted to the East, leaderless, old-fashioned (10) ORIENTATED {ORIENT}{dATED}
14 A hardy bed dismantled in Indian city (9) HYDERABAD*
17 Appetisers in ship contain sour irregular pear (8) STARTERS {S{TART}{pEaR}S}
21 Humiliate cardinal who protects the meek partially (6) DEMEAN {DE{MEek}AN}
22 Scheme for alien on Earth, say (6) PLANET {PLAN}{ET}
25 Extreme letters from daubers (4) UBER [T]
Reference List
Left = L, Conservative = C, Ship = SS