I do not at all approve of forcing teams to return to their league center every price change. Some leagues take time to fill.
I do not at all approve of capped leagues playing with different salary databases. No, all teams need to be on the same playing field. I would be absolutely ticked if I paid more for the same player than someone else did, in the same league.
I do like the solution of locking in prices at league creation. Perhaps generating a number at league creation, rather than at commissioner's entry into league, would help with this -- because commissioners often "pick 12th" or similar in many themes and thus half of the teams can be built before his/hers. A league should be locked into a price structure as soon as possible.
The above, to be applied to open leagues, would likely require them to be treated more similarly to theme leagues, in that people would have to see a league number and thus the database for that number. This might also provide an opportunity to provide open leagues at multiple caps.
Progressive leagues sometimes use salaries to set draft order. Locking in salaries would help with this as well, the actual salary would be included. It would still cause a problem for many owners, however. For instance, I have an excel spreadsheet with the entire remaining careers of each player on my progressive team, including their salaries, so I can make determinations on whether to cut them or not as things progress. Dynamic salaries could really screw with this. For this reason, I like the idea of allowing themes to use the current salary database as well, avoiding dynamic pricing, and would encourage progressives to do so.
I don't care as much as far as how often the salaries are updated, as long as you provide leagues with the controls necessary to avoid the issues I mention.
I am concerned, in the short run, about the poor quality of bench players that may be seen in the first few update cycles. Often teams run the same sets of bench players. Their salaries would skyrocket and leave even worse players available to warm benches. Of course many don't use their bench anyway in open leagues, using AAA instead and possibly waiving some 200K players, so maybe this isn't a huge issue, especially with the +/- % limit.
How will the waiver wire affect this pricing? For that matter, how will the waiver wire interact with dynamic salaries when you "load" players onto it? Maybe you should do away with the waiver wire, I'm not sure you'll get too many complaints -- experienced users generally only use it as a dump for 200K players in leagues with AAA, and it serves as a trap for newer owners to waste money on.
It has been mentioned in here, but beware of how progressive leagues and theme leagues where everyone takes the same players can skew results. For instance, if there are 10 progressive leagues running in 1975, in full or in part, next update there's a good chance that all/most 1975 players are way overpriced.
Consider $/IP and $/PA floors to prevent short term Dupee Shaw Effects. As much as we loved Dupee, it did make aspects of the SIM too easy if you knew how to use him. (Perhaps this isn't necessary, as the limitation on +/- %age will take care of this)