I like the idea of having specialized worlds in the game, may add certain complexities and/or at least make the AI's life much easier which would then be able to provide a better challenge.

However, I more-or-less already do that in galciv2. Granted, it's not possible to have a "food planet" but I wouldn't use it anyway.

The ideas of specialized tiles was to, themselves, add another set o' complexity and decision-making into the game. I quite enjoy not having "perfect games" each and every time. I wouldn't play it as often if everything always turned out perfectly. What would be the point?

On the tile note...

There is another game that I think has a pretty cool tile system.  Ascendancy.

In Ascendancy, you have five tile types: green (food), red (industrial) blue (research) white (generic) and black, which can be terraformed to white.  Different world types have a different mix of tiles, and there are several world sizes, which have an increasing number of tiles based on size.

The blue, green and red tiles essentially add a +1 to production of structures that produce that resource.  So an agriplot that usually produces 1 food unit would produce 2, an Artificial Hydronifier produces 2 (3 with green), and a Megaplex produces 1 food (2 if green) as well as 1 industrial and 1 research.  Other tiles are similar.

IF this concept was translated to GalCiv, essentially you'd have multicolored tiles, from the generic tile to the agri tile, resource tile, research tile, happiness tile, influence tile, etc.  Instead of having a few special tiles, you'd have a mix of these on the planet, based on whatever factors you chose (randomly determined, based on planet color, etc.).  Building a sympathetic structure on these tiles would increase the output of that structure, similar to now, but not as dramatic.

Note that all planets would have a mixture of the various tiles, with certain planets having an emphasis on particular tile types.

This also would encourage the use of 'muli-use' structure, such as a research park that produces both manufacturing and research.  And complementary techs would be required for those multi-use structures (i.e the structure is added to your build cue when both techs a from tree a and tech b from tree b are researched).

The 'marginal' tiles would probably not be special when they are terraformed, but perhaps they could be, depending on the planet type.  This might also make exotic planets more attractive, if they have an abundance of a certain tile type.

So you might have a 'red' mineral rich planet that is ideal for manufacturing, a blue planet which excels at happiness, etc.

You get the idea.  This would make planet building much more interesting I think, and perhaps a just little less like a slot machine...