Roads, I suspect that there are almost as many different ways of enjoying Simutrans as there are Simutrans players, and the more that that can be extended, the better. I understand your concern about development priorities - it is a matter of sharing development time amongst different features, not all of which will be of interest to all players. I was considering coding some of the advanced features myself, leaving the main developers to do nothing more than test them and add them to the main code (although some of the more sophisticated additions I may not be able to achieve without some assistance from the main developers).
I think what Combuijs suggested was not to have an "advanced" mode at all, but just put all the "advanced" features into the game as options that can individually be turned on and off, which would add flexibility, and which would be rather easier to code than adding a whole new mode of play.
Incidentally, it is very interesting to me to see the different ways in which people like to play Simutrans. I tend to play Simutrans (except when testing, which is a different matter) with freeplay off, with obey chronology on, and tend towards large, complex and interconnected networks, with particular interest in rail networks. I tend to like playing from the mid 19th century to the modern day, and am particularly fascinated by the idea of historical trends that have shaped real railway/transportation networks independently shaping my network in the game, even though I am playing simply with the aim of maximising profit and/or service quality. I am very keen on simulation games with complex and interesting emergent properties of the various layers of gameplay, especially when those emergent properties are highly realistic and make the game world turn out very much like the real world, without the player being motivated by anything other than success as defined by the game (even though the player's decisions end up being very similar to the decisions of people in the real-world equivalent situations). I like games in which the player can succeed without excessive number-crunching, where the player has to deploy heuristics in order to make good decisions (because the raw numbers are too complicated and/or hidden from the player for number-crunching to be the most successful strategy), and especially where those heuristic decisions are exactly the same heuristic decisions as would lead to success if the thing that was being simulated by the game was real. The "advanced" features that I have been suggesting, therefore, are, perhaps unsurprisingly, features that, I hope, will tend to make Simutrans (at least, with the appropriate options set) tend more in that direction.