I've worked for tourist RR operations for the past 25 years on and off as a volunteer. They were always on the verge of financial collapse for the same basic reasons...
1. Insurance costs - liability insurance in the $20-$30,000,000 range cost around $30,000/yr. Even paid monthly that's a huge expense, especially if you are only operating seasonally.
2. Run by Railfans not Businessmen - the guys who were in charge loved trains, but had no clue as to how to run a business. Marketing didn't exist, technology knowledge didn't exist. Good example...the last operation I worked for out west spent $1,200 on a credit card machine from their local bank they could have bought on Ebay for $80. Another example... a customer calls in and says they have a tour group of 50 people. They want to fax over all the names and credit card payment info. Employee says "we don't have any computers or fax machine here sorry" and hangs up. I saw this stuff constantly.
3. Terrible Customer Service - screaming at passengers, rude employees, employees not showing up, employees fighting in front of customers, unprofessional employee behavior in front of customers.
With good capital investment, good service, and most importantly great marketing, I"m sure the line to Lambertville would be sucessful.