If you mean by "good investment"; a solid place to put your money in the hope of higher re****s and good profit.....then no.
If you mean by "good investment"; a way to get the stuff you want for a bit less cash.....then yes.
These bottles are standard core expressions and globally they are widely avaliable to anyone, so they are not going to be returing you a lot on the re**** market, the only exception could be the A'bunadh as you may get someone willing to pay a bit more for a specific batch, given it's small batch stuff.
....if you want to stock up in the hope that when you next want a good ol' dram you're not going to have to pay that bit more, then yeah go for it. I get the feeling that the market is going to start correcting itself over the next few years though. The nature of boom and bust is that eventually it's going to bust and prices of standard expressions will fall again. Probably once the supply/demand issues levels out......
I've noticed a massive drop recently in Yamazaki 18yo; it was retailing for around £120 a bottle in the UK last year and now most places are ******* for just under £100 - so a 15-20% drop in price.