Multi-tip lines provide versatility for the angler without spare spool(s). Small loop-to-loop connections between the running line and the tips won't hangup in the guides/tip top.
If you have have an intermediate line for the 10wt, most 9wts will handle it. Or, since you have a 9wt sinker, an extra spool for your 9wt reel outfitted with an intermediate line would be a great apprroach. That would outfit you for the majority of striper presentations.