I appreciate that you are considering yout options conncerning the game, but  I think it unlikely you will get the answers you are looking for.

Whatever money any one has spent has gone,and is not retrieveable.its like buying shares in a company that goes bankrupt, or your piece of technology becoming obsolete.

The game will only run for as long as they wish.

The idea of spending money on the game as an "investment " is a ridiculous notion.

I recommend that you time your Mega-Pack offers (91 days) to end on a major Holiday when the Bank Offers are the best. Then you get about as good a Mega-pack offer as you are going to get. Save up at least $185 US dollars. You then buy the least expensive offer-and then it doubles. Buy that one and it doubles again. And so on.... for me it is like this. $5 dollar Bank Offer--BUY: that doubles to a $10 dollar Bank Offer-- BUY it; that doubles to a $20 dollar Bank Offer--- BUY it; That doubles to a $50 dollar Bank Offer-- BUY it too; and that doubles to a $100 dollar Bank Offer-- BUY that one too.

These all total to $185.00 U.S. Buy all these and you can have fun for at least 6 months if you are frugal with all the good stuff that you get in the Bank offers.

Or you can pick and choose a bunch of $5 and $10 offers and get a little of each. I did this the last time I got Mega-pack offers and I wound up with 40 million gold and a whole bunch of goodies for doing a lot of different things.

If you want to run with the big boys you are going to HAVE TO spend some money for Major upgrades to your town. If you do not mind staying at the level that you are at , and are content to do things slowly, really slowly, then just buy Mega-Packs once or twice a year.

Freddy Mercury wrote

I must also warn people that Mega-Packs are for your Main Town only. If you use an alt' account for Mega-Packs then Plarium considers this cheating the system. When people cheat they ruin it for others who play by the rules.

How would you know this to be true? 

Surely it must just be speculation?