Yes aftermarket cross bars would be much better. Even with a basket as mentioned above the stock crossbars are marginal, especially at this age. The problem with them is the crossbar is thin oval section and the clamps are plastic with the crossbar slid over the end and held in with tiny phillps screws. Mine are bending and stretching the crossbar right where the plastic end cap slips in. Eventually the plastic end will break off or the crossbar material will stretch and crack enough to allow the end cap to drop out. I have a full rack and intend to pull the factory rails off altogether and make new mounts directly to the roof. I have my crossbars close together with the tyre strapped to both evenly, a small half size basket would not make any real difference to the way the bars are loaded as the factory bars are also arched so a basket would load the centre or flex the bar on the ends to flatten it out.
Have a look at the grand cherokee pics thread in the sticky section, there will be plently of inspirational pics there.
Here's mine anyway: