Is "Investment value" always higher than "Market value"?

No. It seems counterintuitive and most people automatically assume that investment value surely is  higher than the market value, since - in the end - it is investors that determine the market value, or should I better say the price.

Market value is - to put it in simple terms - the value that could be achieved, if the company was sold on the market to any (and not some specific) market participant. It of course depends on a number of factors, among which are also the number of interested investors etc. Now, assume you have an investor who already owns 100% of a certain company. They engage you to do a valuation and determine the market value of their ownership interest in the company. Then they also want to know what the investment value is, because they've heard that investment value is even greater than market value. However, investment value depends on assumptions put forth by a specific investor. Let's assume this specific investor has a plan for this company, on the basis of which they will earn very low returns, while investing a lot. Utilization of the assets of the company would be far from optimal. So, the value you arrive at is in fact lower than the market value, because market value is determined by what market participants observe could be achieved with the assets of this company, i.e. they could earn much higher returns. 

So, you go back to the client and explain that, ehm, investment value is lower than the market value because of the way you manage the company...oh joy, don't you just love these conversations?

Another example is that an investor is a company that puts great emphasis on the local environment and people and one of the values they hold dear is to provide jobs to the local population. Even though any rational investor would rationalize their business operations. And this is something that you can hardly put into figures. So again, investment value (for such an investor) <>

So, could we find a way to put this soft stuff, that some investors are so fond of and that actually are one of the driving forces behind their motivation to do certain transactions, into specific numbers and attach monetary value to it? Then perhaps we would see that investment value indeed is greater than market value, even for such an investor. Well, I can just say good luck to those who try and congrats to those who succeed (though I don't expect to see many of those).