Okay, I think this is a seperate card idea. It sounds interesting, especially because you can end the game without any Victory cards. Also the "pyramid" structure and the question when to call your cards is interesting. You could add some flavour and then open a new topic for it.
For Marco Polo, I wanted to keep the cards as elegant (simple and thematic) as possible while having the upgrading tricky but not too hard.
Marco Polo (Action-Traveller) Cost:
You may put this on top of your deck. If you do, +.
When you discard this from play, you may exchange it for Board a Ship.
Two of these with the +card and +action tokens on the pike give you infinite money. Add the +buy token and you can just pick up the entire Supply.
Theoretical considerations of virtually impossible edge cases are fun but practical relevance is the only thing the matters for actual games:
Ignoring Teacher this is conditional on both Events being in the supply. If you play with only 2 Events, as it is recommended, it is not possible to actually get the +buy token. But even if you play with 2 Events the chance to get precisely these 3 Events is 3/20 * 2/19 * 1/18 = 1/1140.
So you either need to play Teacher 3 times or you need to have the 5, 6 and 8 to trigger 3 Events. If you have achieved any of these you can more or less gain a shitload of Provinces or Colonies with any deck.
Interesting point. If you play only non-random sets, this could be an issue. Although tristan is right that it is quite hard to pull off with currently available cards.
Maybe Marco Polo could be a Treasure? But then you wouldn't have a guaranteed terminal for Board a Ship.
Or we could dump it and start with Board a Ship directly, maybe adding another step on the way.
On the Silk Road (Action-Traveller) Cost:
+1 Action. Discard any number of Victory cards and add up their total cost in . If they cost...
to : +1 Card, +.
to : +3 Cards.
More than : Exchange this for Visit the Khan.
Here is the biggest random factor. Not only is the randomizer effect bigger than with typical Tournement (which I find absolutely dreadful, even if I win the race), this is just the Province race to the luxe.
This. Basically Tournament on steroids.
I don't think so. In a card game, when you have to bring together multiple cards from a bigger group, it should be less luck dependent than matching up 2 single cards. (Same as with rolling dice - the more dice you use, the more likely you are to hit the expectation value). Sure there are still freak values, but they are rare.
It is very very unlikely to draw On the Silk Road with a lucky early Province + 2 Estates if you didn't prepare for it somehow.
But by buying into this chain, you'll be slower to Provinces unless you've had a good plan all along. Also, if you actually think about the effects, they aren't that amazing.
0-2 = Peddler. You don't have to discard for this so it's always available.
3-10 = Double Lab. That sounds amazing until you remember that you had to discard cards for it. You draw 3 cards, but you're also discarding at least 2 cards! This makes it barely better than Cellar. Possibly worse, actually, since you can't discard Copper to it.
Hum, I intended it to be strong if you don't exchange it. You could also discard just one more expensive card to get the double Lab. Should it be stronger?
Maybe: less than 10 = draw twice the number of cards you discarded?