SS, I fish the party boats a lot. What you were told is correct, and thats why I use mono. THe one downside of the party boats is that tangles are inevitable, so you want to do what you can to minimize the downtime. The reason they cut the spectra first is that once tangled, esp. in small diameter, it is just about impossible to untangle.
What I do is fish spectra as backing for some line capacity, and then add 150-200yds mono on top. This is longer that most, but it makes sure that your line in the water (and therefore the line subject to tangles) is mono, not spectra. I would get some berkley Hi test in 20#(rated to break at 39#) or better 30# (rated to break at 50#). Put about 150yds on top of the 50# spectra you have. I like to have at least 400yds on an offshore reel, so you may have to experiment.
As a guide, I use a line calculator to estimate the two capacities. For example, if a reel holds 500 yds of 50# mono, and I want to fish 60# line on it. I will back with approx 300yds of 80# spectra. THis line has the diameter of 20#mono. So I use the line calculator to see how much 20# line the reel holds. I subtract the 300 yds capacity the spectra will use, and that tells me how much 20# capacity is left on the reel after I put the spectra on. I then use the line calculator again, with 20# entered and the remaining capacity, and enter 60# mono to convert. That then tells me how much 60# mono I should be able to top off.
You can play around with this and find an optimal capacity for what you want to put on any given reel. When I am buying a new reel, I do this also to see if I can get the 300yds spectra I want and 200yds mono. If not, I need a bigger reel.
Hope this is helpful (maybe to someone).