Dick,
Well, since I'm a Dispatcher I work the same line all the time. I rotate between two desks. One week I work mornings on the Hawaii/Mexico desk and the following week I work afternoons on a North Atlantic/Europe desk.
As far as pilots go, it all depends on what they bid each month. If you have enough seniority you can fly a shuttle line and only fly back and forth between LaGuardia, Boston, and DCA all day long with weekends off. But, if you're a new guy with low seniority then you get stuck with being on reserve and subject to being called out at all hours of the day/night to fly whatever needs flown.
As Dispatchers at US Airways we only bid once per year. Pilots will bid every month, and what they bid depends entirely on what "works" for them that month based on outside interests and responsibilities. If seniority allows, maybe one month picking up a line with weekends off works out ok. Next month due to some family obligations maybe bidding a line with Tuesdays/Wednesdays off works better for the personal life. Some senior guys will bid to fly European trips in the summer when the weather is nice there, and then bid to fly Caribbean trips all winter. But, you have to be mighty senior to be able to do that!
Simulated Airlines will never be able to fully capture the scope, nuances, and complexities of bidding for schedules, but we can get "close enough" for our purposes. As you mentioned, it would be more realistic to fly the same set of trips for the month vs just flying random trips. Years ago when we were America West Virtual Airlines we did in fact try this concept, and it was pretty much met with open rebellion. Even though it was more realistic a lot of guys did not like flying the same 6-8 trips all month.
You also made a very valid point when you said you would get more proficient with each flight. By flying the same set of trips for the month you would get very familiar with the company route, the published departures/arrivals from the airports, the terrain and any special approach procedures involved, etc. Every trip would still be unique because the weather would be different, traffic flow may be different, the aircraft condition may change (MEL's), etc.
Personally speaking I would like to eventually see a bid procedure in place to where crews are in fact flying the same set of trips for the month.
Or, if we can work out the logistics maybe we'd do a bi-monthly bid to where you'd fly the same trips for two weeks, then bid for the last half of the month again. Quite a bit to think about and work out.
Mike C