I have the same... I've stopped building decos where possible because my Amusement Park is (for all intents and purposes) the last thing that gets polished by aid - despite the fact it gives a huge amount of Happiness
Ostensibly the claim is that mot/pol is random with a weighting by descending age, though I'm pretty sure it's not strictly enforced that way as I've often ended up with a non-motivated PE King and a motivated CA one.
It was said at the time aid was introduced, and many times since, that decos should be ignored until there is nothing else left to polish. I don't care if I get an extra 300 Happiness from a Lichen Lamp if I have several thousand points sitting there on a premium cultural that happens to be a few ages old.
My personal opinion is that the Offered/Wanted Goods section in the user profile (where you can list three specific goods) would be better off being replaced by three option that say "Coins/Supplies/Polish" where you can set an preference for the order of aid. The Offered/Wanted bit is currently nigh-on useless, and the Aid teature is much more active.