Just so we're clear; there is NO such animal as an investment VISA.
Just like there's not a retirement, marriage, supporting children visa either. Those are all types of extensions of stays based on having held a Non-Immigrant Type O <-(other) visa.
I know of only one person on an extension of stay based on investment but he's grandfathered in the program at just 3 million baht invested (because he started getting the investment extensions prior to 2006).
He came in back in 2004, transferred in 3 million baht into a thai bank, promptly applied for a 90-day, single-entry Non-O inside the country based on investing, and during the 90 days permission to stay stamp on that visa invested it in gov't approved bonds. He then applied for his yearly extension of stay and has been getting yearly extensions that way it ever since..
BTW; he's now 48, so when he started this he was only 36. He said he's never had a single hiccup in his yearly extension process and isn't going to change it until he hits 50 where he'll change the reason for his extension to "in the instance of living out the end of your life" <-(called retirement by every Tom, Dick & Somchai)..
Now that the investment amount for this extension has been raised to 10 million baht, it would behoove anyone contemplating going down this route to really look into the particulars.
That's all the first hand info I've got.