Equals wasted money
Platinum has a higher resistance than Gold, Silver, Copper, and even Aluminum!
It is a marketing gimmick to get ignorant people that think "Hmmm Platinum it must be better" to spend more money.
As far as the silver solder goes it only has 2.5% silver in it...do you really think that 2.5% can do much at all to reduce the resistance? Actually most silver solder is made of silver and antimony....mostly antimony. Antimony has a higher resistance than lead or tin so its quite possible that silver solder has a higher resistance than regular solder. Silver solder wasnt made to decrease resistance, it was made to make a stronger mechanical connection.
Your best bet is to get silver plated copper bars, the resistance of silver and copper are very very close, the reason for the silver is for corrosion protection. The reason good stereo plugs etc use gold is that it has very good resistance to wear and corrosion.