Here's my uneducated opinion:
Spot is spot and as long as people desire silver there will be buyers for it, no matter what the price.
If there is a massive rise silver, it will start to make it into the MSM.
Once that happens average Joes who have never bought PM's before will flooding in to their local bullion dealer hoping to grab their slice and make a small bundle speculating that the price will go even higher. Afterall that is what the MSM is telling them, and if it's on tv it must be true.
So that local dealer is now going to be in the market for large volumes of immediately marketable product. It now comes down to supply and demand. If I walk in with a bunch of well recognized (think Perth Mint and PAMP) silver bars in good sale-able condition that the dealer knows he can immediately put on his shelf and sell by the end of the day he is certainly going to be a buyer.
Even if he only pays me spot for it, I have made a tidy sum by buying before the rise (ie:now), sure I could sell it for a few extra percent on here, but that takes time and effort (replying to pm's, trips to the post office etc).
What you have to make sure you are doing is stockpiling stuff now that will be marketable to the average Joe in the future. If silver goes to $100/oz, a 10oz bar will cost $1000+ and a 1KG will cost $3215+. IMO 10 ouncers will be the limit for the average Joe's budget. Sure there will still be some willing to drop $3k on kilo bars but volume will be in 10oz and smaller.
Personally I stack 10oz exclusively (except for 1 solitary 1KG - hey, it's nice to fondle sometimes - like as I write this). To me right now 10 oz represents the best tradeoff between premium and future liquidity.
Would I personally be buying silver @ $100/oz - HELL NO, I would be selling and then re-buying even more once the bubble bursts.