I think you need to array the truss instead of placing multiple trusses and dimension them. If you use Array, they are grouped, so you can change all trusses in one click, and you can easily change the spacing by changing it once and it will update for all instances.

Personaly, I hardly ever use beam system. I find that simply arraying or even copying and Dim w/ EQ works just as well. Martijn is correct though. You need to array your truss.

Agreed, I don't like the beam system for much other than flooring joists.

With trusses I usually group the lot and copy the group. The reason I do this is that I like to trim up and cope my trusses first so they look nice and neat. This usually involves unpinning elements in the truss, so if you don't group them, and array them instead you get this ugly problem with the analytical lines all pointing to the initial location. I don't use analytical model at all, so for me both methods work, but if you are using analysis software be careful when you copy or array trimmed up trusses, they do not behave nicely.

Also I find that if my roof extents change, or some element supporting load is moved causing a modification in the truss, I only need to modify once rather than re-do my array, or clean up every single truss.