Spectacular ego, heart lost in the system (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

E[g]O in METRIC [system] 2,17 TUBE STATION : BEST [most efficient] + AT in [breaking] an anagram [depravity?] of OUT IN 3,15 GLOBAL ECONOMY : GLOOMY [pessimistic] around [about] BALE [to package] + CON[servative] [Cameron’s party]: definition: ‘worryingly precarious thing’: a beautifully constructed [&lit?] clue which raised a wry smile, which might have been a laugh out loud if it weren’t so horribly topical 4,19 ICEBERG LETTUCE : cryptic definition 5 TABLE MAT : reversal [turning up] of MELBA [Dame Nellie, ‘sweet singer’] in [to plug] TAT [rubbish]: I’m not keen on the definition:  ‘this is flat’ 6,26 MORNINGTON CRESCENT : anagram [fixed, i.e ‘rigged’] of TERMS NOT CONCERNING – and it’s a TUBE STATION 7,8 BANANA REPUBLIC : anagram [unstable] of INCAPABLE and URBAN: I spent too long trying to make an anagram first of STATE INCAPABLE then REQUIRING URBAN 13 WINDBREAKS : WINKS [bats] around [nipping] anagram [unruly] of BEARD: I think ‘bat’ really needs ‘an eye[lid]’ to equate to ‘wink’ but I liked the clue. 16 MARINADE : MARE [horse] round [on the outside] I[ncline] N[early] A[lways] D[ownhill] [first letters – ‘for starters’]; the definition is ‘steep’, so this is another nice ‘lift and separate’ clue, like 24,21 [‘losing ground’] 18 ONE-ON-ONE : O [oxygen] + NEON [another gas] + O [oxygen] + N [nitrogen – another gas] + E[nergy] 24 LICK : double definition