So would the increased risk diversification be worth all the cons?

That is called a diversification exchange and is a great way to expand your portfolio. 

At least with the REIT's you get diversification and the minimum is very low.As far as pooling money with others, all people in the deal have to be accredited.

Now I have 12 units (multifamily buildings) in my living-area in germany - 2k€ monthly passive Cashflow + repayment of property loan (and I have high returnrates).I was thinking about diversification of my portfolio and I’m very interested in US real estate markets (lovin the US – made vacations in Cali sooooo beautiful over there!).

@Derek A GriffinInvesting an IRA into real estate is purely a diversification play. 

I absolutely would love to hear more about the benefits of a SDIRA... and you driven the nail into the point that I was wondering (IRA's are good for stocks and bond investments while SDIRA's are good for investments in other vehicles, ultimately making it beneficial to have both kinds of IRA's for diversification purposes.)I will definitely reach out to you to follow-up in the near future.

When I went to expand to other areas for diversification I found it much more challenging. 

Private real estate offers many benefits to individual investors, such as high returns, portfolio diversification and tax efficiency.

Shawn.Duplexes and single families and quad's all work in the same way and you should have a little bit of diversification in terms of location and product type. 

But I'm in a 800,000+ MSA, not a "company town", so there's sufficient diversification of multi-industry employment.