Personally I would be willing to keep all my dollars in the Ripple system because I see the combined effect as net positive.
I would never keep bitcoins in the Ripple system though, because that just adds counterparty risk without adding any compensating benefit.
Unless, of course, certain people are successful at keeping Bitcoin limited to a cripplingly low transaction rate to artificially make blockchain transfers slower and more expensive.
tl;dr:
Ripple makes dollars more useful.
Ripple makes bitcoins less valuable.
if (Ripple makes dollars more useful.
Ripple makes bitcoins less valuable= true);
then
{what does XRP do?)