No. Its affect. Curse never has a good affect on a deck. Ambassador/Fairgrounds/Piles dont matter.
Adventurers affect specifically deals with treasure, wereas curse deals with nothing.
Meh, this is just definition lawyering with the wrong form of effect to boot. The effect of adding a curse to your deck can, in sufficiently constrained scenarios, be quite good and superior to any other legal option.
Curse has the following innate advantages:
1. It is free.
2. It is low in quantity.
3. It is not of the same card type or name as anything else in the game.
Start with the third one. Curse works just fine for powering up Harvest. If you can draw your deck (thanks to some trashing) and discard cards (e.g. Horse traders), then buying a curse for nothing can give you 3 unique cards without using coin. Each play of Harvest can net an additional coin off the curse if you have nothing but your 3 or 4 unique cards in the discard. Say you intend to use a draw the whole deck (you used Loan to thin the deck), Tr -> Horse traders away 4 cards, and then Tr -> Harvest (discard Curse, Copper, Loan, Estate) for a whopping 14 total coin. In a tight deck, that curse increased your deck value by 5 (and increased it by two compared to buying a copper. I can't say I've done it often, but I will consider buying an untrashable curse if I'm going for a big engine with discard/Harvest as payout.
Next take the second, for a City deck, buying up curses can empower a megaturn. Say I have Kc/City deck. Buying 10 curses sucks up 10 card of draw (assuming no curse trashing), but I gain up to 27 cards worth of draw by activating my cities; each curse makes my potential fully drawable deck 1.7 cards larger. Activating the second time makes my deck potential 27 coin richer as well. This, of course, ignores the very useful quality in a deck of being able to end on piles with a lead.
Need a card for your Hermit or Jack to trash? Curses are free and unlike copper they can be trashed by things that can't trash treasure. Take something like a Hermit/Madman/Market square setup, a deck with two curses can have up to 9 more coin potential (trash a curse instead of Mrksqr with one Hermit, gain an extra gold; trash the second curse instead of a second Mrksqr, gain two more extra golds).
//end obscure debate
The real problem with Adventurer is not competing with gold, it is the limited timeframe of most games. By the time you can get Adventurer setup, 6 VP a turn will rarely net you a win. Getting over the 6 VP a turn hump is pretty hard outside of Colony games - you need something to trash down your coppers; then you need to build economy up to hit 6 (e.g. 3 silvers) and then you need to buy more treasure/Adventurers to ensure you hit 8 ... or you need non-terminal +buy to to get over 8. Adventurer just tends to be slow to setup and if the game lasts that long it is there are powerful attacks (conflicting with Adventurer as terminals) or because there is an even more powerful engine out there.
One combo I have had some success with is Forge/Adventurer. This needs an early lucky 7 (paging Mr. Baron), but if you do get a T3 7, Forge can eat all the coppers and turn 3 estates (or an estate + a four) into a gold. If you opened Silver/4 then you just need to buy an estate, Forge everything but the silver into 2 golds, and then buy an Adventurer. Pretty much, every turn you draw him becomes a province and when you miss, duchies aren't too terrible.