Viserys putting the Targaryens back on the map was their original plan, which of course was screwed up (thankfully) by Viserys being an insufferable cock. With him dead their only hope of restoring the Targs to power was with Dany, which they soon realized was a much better plan when they took notice of what she was doing post-Drogo.
I don't think you can say for certain that this was the plan since they always had Aegon in the background. It's possible that Viserys was the original goal and Aegon just the backup, but given how emotionally and philosophically invested Varys was in Aegon when he killed Kevan, I don't think that's likely. It seems more reasonable that Viserys was a tool to either build an army while Aegon was kept secret that Aegon could take over later, or that they were aware of how awful Viserys was and his job was really to launch a brutal invasion with a barbarian army so that Aegon could be the hero and save everyone from it and build his popular support that way.