Yep, we've got a broken monorail diecast "toy" too. My poor fellas - they still play with the three parts! It was the plastic connections between the sections that broke. My boys loved riding the busses, trains, and monorail. We bought theme park busses in diecast, maybe 7 inches long, a couple of small train engines maybe 4 inches long. We also like the "ride specific" toys, like the Test Track car, Buzz Lightyear in a Spaceranger Spin car, Pooh ride, etc. They sometimes talk about the rides when they play with them. They take them here and there and they know that they are special and that we can't replace them until our next trip, so they take good care of them. I think their favorites are the busses. They can play with them and clean them up in a hurry instead of going through a major set up of a track, etc.
My DSs also have the whole wooden train table setup, and I would definitely buy stuff if they would make it compatible to the Brio/Thomas stuff. At a toy store recently I saw a three piece train that looked like a wooden version of the monorail, but it had black wheels on each piece. It might have even been Brio, I can't remember for sure, but it was $19.99. I want to say it was called a "high speed" train but I will have to google to check it. I have to go back and get it when DSs are not with us!
ETA Ooops - I googled it and apparently it is a Brio High Speed Train 2-piece set with sound.