Is there any advantage to pouring a thicker concrete slab for the basement?
Before I'd add more concrete I'd add reinforcing - reinforcing is cheap and the benefit of it is huge, .vs. unreinforced concrete.

After that it's a matter of use. Will you have a machine shop in the basement? You might want a bit more thickness, too. Will you be playing ping-pong and/or putting in a 1970's basement bar? No benefit. Woodworking machinery? 4 inches is probably plenty. Storing random junk you probably should throw out? Your wine collection? Minimum thickness is fine.

An additional consideration (has not much to do with thickness) is whether you might ever want heat in the basement - in which case, installing radiant heat tubing in the floor, and insulation under the floor and around the outside of the foundation walls is another low cost upgrade with major benefits, if you get it done in the planning phase.

Yet another consideration: Installing exterior drains at footing level is trivial when the hole is open (just the cost of the pipe and placing it - perhaps one more trench to take it away from the house) but terribly expensive if you discover a need for them later on and have to excavate...