On average a UR+ card will be slightly stronger than a UR card, but it's a pretty minor difference. Mostly what makes a UR+ card the more valuable of the two is the skill animations or moving pictures that come with them.
personally, it's hard to get a UR+ card to go to level 150 in short time most importantly if you're a f2p that can't purchase vip.. but it's depends on you to level up or just wait for another UR+ to come home^^
