I've sailed in a Studio twice, in 4 cruises on NCL. One time that I didn't was because the ship doesn't even have Studio cabins (Joy). The other time was that when all other costs were considered the balcony was only about $60 more than a Studio so of course I was going to take the balcony!
For my next cruise a regular inside cabin was several hundred cheaper than the Studio, there was no solo supplement. When I talked to my PCC to book she asked if I really wanted an inside instead of the Studio, when I suggested she look at the price she realized why I made that request and booked it. Plus, for as much as I do like the Studio, for a 15 day cruise I think I'd like the extra space a regular inside offers, even if it is only 30% larger.