I have always been wary of letting others into my town, however people on this forum are generally trustworthy and if you give them some incentive (I gave pink roses to people who visited my town multiple times) you shouldn't have much trouble getting the upgrade. I just had people literally come to my town and then turn around and leave, and there were a few super friendly individuals who did it tons of times and didn't request anything in return. So overall, I would just make a thread in the "Train Station" forum saying you're x amount away from getting the upgrade, and you'll find people willing to help who aren't going to go wreak havoc in your town. Good luck.
I have the fairy tale station upgrade and I love it.