Considering the price stays fairly steady, meaning that by the time you are finished mining and sell it you will only have a small loss (if any), ANY EXTRA XP that it gives is worth it.
But yes, it gives faster xp and for the reason stated above it is worth buying a D Pick.
I have to be honest, from my stand point it dosen't matter because it cost what like 14m? I buy random shit like i'll put 10m into welfare pk sets i never use.. so if i was gona mine your damn straight i'm not wasting any of my valuable time.
Logically your not wasting 14M cash your just making it into wealth. I doubt the D pic will drop too much from the time you buy it to the time you sell it.
Well, not only will you be saving ~15% of the time mining (so, if you get say 10M xp with a rune pick, you would've gotten ~11.5M xp with a dragon pick), you will also get the gold ores needed faster, which means a slightly higher profit/hr.
And as mentioned, you can always sell it back again.
iv got 99 mining on 2 accounts now, and yes its definately worth it in my opinion.
Ditch the rune and go for dragon. Its not like your losing the 11m, i even made profit off keeping mine for a while.
Even if you lose money by the time you sell it, that extra 10% of time you save getting 99 will allow you to make back any difference in price that may or may not have existed between the point at which you bought the pick and the point at which you are selling it.
Isn't is supposed to save like 40 hours of mining time using rock caverns? (fastest way to 99 mining I believe)
So with 40 hours extra you could use another money making method making millions and in the end you will sell back your d pic for probably the same price.