2X to hydraulic lifters going on forever w/o failure. Modern roller lifter engine designs as mentioned have hundreds of millions of miles (if not a few billion, no exaggeration if one does the math) of hydro roller success.
And yes, starting out anew makes the cost less, even though nobody every said rollers were cheap! And while I do agree a well-broken in flat tappet lifter will last darn near forever, there have been way too many cam/lifter failures as noted on all of the American engine related websites (BBC, SBC, Dodge, etc.) just like this one. Today, many elect to go roller simply because, even doing everything right, they don't want to be one of those with a worn down cam lobe in a brand new rebuild.
I do have one beef about hydro roller lifters: added valve train weight does limit rpm potential. Jay has mentioned here a number of times the real-world limits of an FE's rpm levels merely due to this added weight. It's true for other engine makes as well. But, adding beehive springs or titanium retainers or smaller diameter stemmed valves or, most pricey of all, titanium valves is beyond the pocketbook or need for most weekend warriors.