Is there an advantage to having the Origin X1 Baseline over a Velocity or Force? Why would anyone want to use the base model?

It very much depends on what you want to use your X1 for. For the most part, we expect the Velocity to be preferred largely by specialist or dedicated racers, as the lack of weapon hardpoints limit its options for day to day use compared to its variants. With the X1 Force, you can get extra defensive shielding and improved scanning but at the cost of weight and an increase in price; just as the Velocity sheds mass to become a better racer, the Force trades a bit in that department for taking on extra gear. The X1 Baseline may be the most well-rounded of the three at a more comfortable price.