In all honesty, the choice between simplicity and complexity depends on two main factors: 1. what you want to get out of the system, and 2. what resources (time, skill, money, etc.) you have available.
1. What You Want:
How much do you want the system to actually do? Is it necessary? For example, as Jay TenBrink brilliantly pointed out in
this thread, sometimes even a common function such as shifting is not crucial to the game and can be spared from the design process. "If it ain't complex, don't complicate it" (Somebody has probably made that into a quote by now)
Of course, feedback and intuitive controls are almost required of the higher-level systems in order to make the best of their functionality. During OCCRA (local robotics tournament in Michigan), I initially designed a double-jointed arm but did not design the controls or feedback for that system, and ultimately had to scrap it in favor of a simpler stick-arm for the sake of controllability.
2. What You Have:
The more pressing factor will certainly be your team resources - how many and what type of machines you have, the skill level of your machinists and designers, and the funds to cover the cost of unique parts will all influence the decision on design. Given that, it is critical to know your capabilities before the season begins in terms of who's available and if there are any companies you know that might donate services for your team. Knowing the limits of your capabilities will assist you in judging the scope of your project.
My team does not have CNC machines readily available nor any sheet metal benders, so we generally design our parts to be - at the most complex - capable of being made on a standard mill or lathe. Often times, you won't need the ridiculous complexities of an uber-precise system- most everything that was designed like that resulted in a maze of intricate parts. Don't forget the potential benefits of prototyping to determine the viability of a system!
To summarize, what you design will depend on your resources (best if found out before the season starts) and your demands for the system (to be determined after the game is revealed). It will be a matter of where you want to go with the design process this year. Just last week, I was talking w/ Francois (Frenchie on the CD forums) about design complexity, and he brought up an interesting point: crazy ambitions will lead to the students going beyond what they plan and will keep them focus on continuously improving the robot. Every team and every student will have their own challenge to overcome this season.
Well, I think I've used up my essaying capacity for the day, I hope this helped.
_Alex