The trouble is even if this fairly unlikely scenario of large numbers of banks starting to using Ripple came about, there is no direct correlation between the use of Ripple IOUs for things like USD transfers and XRP having any significant value.
For XRP to justify even its current price let along a significant rise, it would need to be used as a market making currency for lots of trades (eg Euro > XRP > USD) but I really don't see that happening when people can just create direct exchange markets (eg Euro > USD) and reduce their costs and risks.
It only costs a tiny fraction of a ripple to do a trade, and I think there's a way to do it at no cost too. If all the banks adopted it the price wouldn't go up because of ripple trading fees. It's unlikely all the banks would adopt it anyway, instead they would clone it and use their own private network.
They may not clone it - Ripple is available, compliant and it works. I doubt they would want the legal headaches involved. I also agree with XRP value - there is no driver for it to gain aside from hype - it's not like XRP represents Ripple stock.
This is not likely to be the case with distributed (or semi-distributed) autonomous asset swap blockchains like Waves, Ardor and the like - in my opinion.