In my experience, people look for 3 keys things buying silver coins;
Authenticity - the legal tender bullion coins from World Mints tick this box, legal tender/coin design/mint tubes - all make them harder to forge, (not that we're seeing much fake silver as yet, but that could change when silver's $50-$100 an ounce!
Local Country specific silver, i.e in UK the default is Britannia 999 silver £2, Canada the Maple leaf, USA Eagle etc
Collectability, any enhanced premium form scarcity, i.e. desirability
Since the Britannia switched form .958 to .999 silver and the Mint went from collectors silver to basically bullion investment silver, there's not really much added collectability value in most of the newer Britannia bullion silver, although certain years and older coins will still get a premium at times. (less so than many retailers will have you believe!) i.e 2013, 2014, 2015 Britannia are still relatively scarcer and can sell for £1-£2 a coin more than a current year. If a collector wants a tube of every year, they're going to happily pay slightly more to add the older years, especially if the silver has been well stored and is still in as Mint condition.
There's also the lower mintage privy editors and oriental borders - all command a decent premium with collectors.
The Dragon 1 ounce 9999 silver bullion bars are very unusual, in every sense, since they tick all the above boxes and people have really taken to them. They look good, they're an unusual design, minted to a very high quality - in my opinion far far better quality than any bullion the Royal Mint produces AND they're quite a small mintage at just 500k for Worldwide sale. That means there's not many at all reaching the UK shores, compared to the unlimited minted Britannia. I'd say there's no comparison from Dragon bars, to bullion like the Maple, or US Eagle, given the huge mintage volume the Eagles are produced at, not uncommon to see 30,000,000-40million Eagles minted per year, that's 80 X more than Dragons!! Even an older nice 1999 Eagle still had a mintage of over 7million coins, compared to a 1999 UK Britannia just 69,394 that makes a 99Britannia 100times scarcer than the equivalent US Eagle.
2001 even scarcer at just 44816 Britannia v 9million Eagles! You can see why older Britannia fetch a premium.
Back to bullion -
As silver prices rise, most premiums of all but the most desirable silver coins, will disappear. i.e. imagine a scenario with silver at £50, most silver bullion buyers won't care too much wether they buy say a 2016, 2020, 2030 year coin and it's unlikely that the 2016 will fetch much different to say a 2020 / 2030 etc (forward thinking!) Same rules will apply, buyers will want the trust and authenticity which comes from the genuine legal tender minted coins, as well as buyer/seller trust of course.
I think they'll still be modest premiums for the scarcer more unusual coins amongst collectors, the Dragon bars should maintain their desirability. Meanwhile, they look and stack nice 🙂
Final thought, in a declining or static market - having added collectability does also have benefits. Personally, I'm happy paying a premium on the Dragon bars. I also appreciate premiums on older collectable sterling silver or fine graded silver coins.
I will do a specific article on various mintages V values
Plus add some Dragon bars into the trade Hubs. Hopefully other sellers will start to trade them here as well at some stage (although since they only started minting in 2018, I'd guess most owners are buyers rather than sellers right now!) 2008 Dragons are also quite scarce, you don't see many at all with UK dealers and they certainly are commanding a decent premium.