Yeah, the better the gloss base, including polishing the plastic prior to spraying your black gloss, the better the Alclad II will come out.
Second point to remember if you spray the very shinny Alcalds, ( Chrome etc.) you need to not handle them with bare hands or only very carefully, until you get a gloss coat ( ie sealer ) over that finish.
The "duller" range of Alclad (aluminium type colors) are more resistant to handling so less likely to rub/wear off.