I think it would be nice if, instead of making it rated, we fixed the actual issue with Bourse Scoring.
The Bourse variant we play was designed to have different people playing the Powers and the Investors. Players would play an actual Diplomacy game, and investors would play a completely separate game and would be unable to influence the players. I believe they would still be able to negotiate amongst themselves, which made it something of a Diplomacy game, but all in all it's not a particularly interesting variant for the Investors and isn't anything new for the Players.
Merging the two roles and having the Players also invest was a genious move and created a Diplomacy variant unlike any other, where keeping on top of information is essential and attempts to outthink opponents in the Bourse would shape the game in ways Diplomacy players would otherwise never see.
The massive issue with this is the way scoring has been adapted - to only include the Bourse side. That means that you personally don't need to do well on board to get a good result. Think that's a good thing because it gives eliminated players a good chance of winning too? Think again.
Players who initially do well on the board (and who understand the game) are *guaranteed* to win Bourse under this system. This isn't because they've probably invested in their own currency, nor is it because they can demand information from people. It's because they can hide small powers away behind their lines.
First thought there for everyone who has bothered to read this far (Hi!) and who has played Bourse is "Of course! Money farm!" but that's not the real issue here. The actual reason is VP farms. Notice that I said those who "initially" did well on board would be guaranteed to win? That's because they don't end the game with any supply centers.
For players unfamiliar with the concepts here, I'll lay out of couple of definitions (if you don't know about these then you'll be at a massive disadvantage going into games):
Money Farms - Keeping a small power with a low currency value alive on one or two SCs, investing enough money into their currency that it rises ridiculously high, and then selling that currency until you run out and finally eliminating that power.
VP Farms - Keeping a small power with a low currency value alive on one or two SCs, investing as much money as you possibly can into their currency, then throwing your SCs to them to gain an insurmountable Victory Point Lead.
Money Farms are very strong, but they have counterplay. Overinvesting in a Money Farm is a big risk of using the strategy - this is where you invest too much, and the majority of your invested cash gets locked into that currency for the rest of the game due to your inability to sell quickly. The problem of Overinvestment can be reduced by buying with Partners, meaning none of you have to invest as much and you can all sell more quickly - but any partner who invests a bit less than the others will be able to make a higher profit and cause a decrease in the profits for the other Partners. Additionally, Money Farms can be countered by careful investment by other players. If you think someone is setting up a money farm, invest 4-5K in that currency (much less earlier in the game) and you'll still make a large profit from it without having to invest anywhere near as much as the other powers did. If your guess is wrong and they don't money farm with it, you don't actually lose a huge amount, and you massively decrease the amount they can buy if they try it on the following few turns.
VP farms have all of the benefits of Money Farms and none of the downsides - the only problem with it is that you need to be in a strong position to pull it off. With a VP farm, you don't have to worry about overinvesting at all, because anything you have locked in that currency is converted to VPs and you can guarantee that those will be worth it by throwing your centers to the smaller power. Additionally there is zero counterplay - people cannot invest enough to prevent your buy, because the amounts they would have to invest to make it not worthwhile for you would be extremely high and would take them out of the game if you eliminated the power. You don't have to go in with partners, because overinvestment isn't an issue. Most of all, though - if you manage to set up a large stalemate line, this strategy gives you an instant guaranteed win, because nobody can stop that VP farm from growing to consume all of your territory.
VP farms are only a possibility because board score is meaningless in Bourse. RUFF's suggestion to fix that (making the game Rated) is okay, but it doesn't entirely solve the problem because it splits the incentives entirely and forces players to choose between whether they want higher rating or higher bourse score. Games scored in two conflicting ways are not great to play in.
My suggestion would be a relatively simple one - merge the Board and the Bourse. Here's how I would do that:
Player Score = PVP + (0.5*TVP*PSC/TSC)
The acronyms stand for:
PVP = Player's Victory Points
TVP = Total Victory Points (the sum of all victory points earned by every player)
PSC = Player's SC count (Since the Diplomacy Rulebook states that in the event of a solo that player is considered to have conquered the entire board, in the event of a player soloing this is every SC for that player and none for everyone else)
TSC = Total SC Count (Total number of Supply Centers on the board)
This way, your board performance accounts for 1/3 of your score, and your Bourse performance for 2/3. This works by essentially scoring you on the percentage of the total VPs you managed to obtain, and the percentage of total SCs you managed to obtain, and combining the result.
The fractions might need some work - 1/3 Board might actually be a bit too much - but in general this system should make the game significantly less broken.