First, there is no longer any specific indulgence attached to using the Pardon Cross specifically. That was done away with decades ago when the Manual of Indulgences was updated and eliminated most of the very specific indulgences.
Second, if we just regard the Pardon Cross as a crucifix to be used in prayer generally, then if you have it blessed by any priest or deacon, you can get a partial indulgence by praying with it as an “article of devotion” (same for any other type of crucifix). If you get it blessed by a bishop or the Pope, you can get a plenary indulgence by praying with it on the Solemnity of Sts. Peter and Paul (June 29). You cannot get these indulgences for using an unblessed crucifix. So yes, you need to have it blessed.
Third, regarding graces, you still get grace by praying sincerely with an unblessed sacramental such as your crucifix in its unblessed state. If you get it blessed, then the additional blessing is considered to be an additional sacramental and you would presumably get more grace as you’d be praying with two sacramentals.
All things considered, just use it to pray with now and then get it blessed when you can.