I personally would not like to see this happen. There would be almost no reason for me to buy MS, sure you get more money, but thats nowhere near being able to actually help you make a good sum of money, sure you get more exp, but it only helps so much, and if you've already gotten a leveled team, you have no use for it, the main reason I, and probably many others, get MS is because of the somewhat realistic chance to find a shiny. The only benefit i could see coming from this is the potential increasing of prices, which would only benefit the people who have been here for some time and have accumulated many shinies which they could then sell for more money, making them even more powerful than they already were. This doesn't benefit new players, it in fact hurts them. If noobs wanted to get MS so they could move ahead in the game, by selling shinies to make money, it would literally be twice as hard for them to do so.
And as for players like me who have done all the quests and beaten all the gyms, this really makes the game less interesting, and therefore would make me less likely to play. Being able to find shinies is very exciting, and considering how few i find with MS right now, i really would not enjoy it being twice as difficult. Aside from tournaments there wouldn't be much incentive to play. Grinding for HRs and shinies isn't exactly the most exciting thing, some people like to do so, but most would agree its just annoying and tedious.
However, if you absolutely insist on changing the Shiny rate, i would encourage you to give having membership more benefits, such as maybe a 2 token discount, or maybe 1 token store pokemon for half price, and keep the 1 token discount. Even maybe increase HR chance by 50% or whatever percent would be fair. Or maybe even increased chances to find items like Metal Coat and Dragon scales, even though they may not be too terribly hard to find already.