I've only played Ireland so far with 3-players. To spice it up, sub Japan Bullet Train action for Irish Locomotive...
After a few games, I'm happy sticking with a fully defeatured locomotive for 3-players. I've also grown to hate the De-urbanization action - too ornery and nasty. I do want to try Ireland with 4-players though.
Barbados - as a 1-player map, replayability may be low, but cube randomness makes it unique every time. Action selection restrictions make for some interesting strategic planning.
St. Lucia - an excellent 2-player map. A very different game with goods starting on every plains and river hex, no goods growth, and a large number of 'stubs' abandoned after moving the goods from those hexes.