Oh, you've got a topic here that I will row into!!
As someone who has plenty of bookmaker accounts and is an avid fan of the exchange, I think we have a great position as a punter, but this is gradually receding as more bookmakers remove Best Odds for many bets. I find it hard to keep up with the T&Cs of each bookmaker, but its imperative to do so if you want to get the best prices.
To answer the question, I find the additional extra place a good proposition for a few bets, but generally if I am betting on a horse to place as well as win, I split my stakes and either bet at Betfair SP, or at fixed odds on the place market.
I find the Best Odds is very useful, and I would prefer that to additional places. Obviously you are aiming to beat the market with a bet, so backing a horse at shorter than SP is annoying. If on a rare occasion they win, then its more frustration!!
My rationale when having a bet is -
Best Odds Available at the time (normally betfair exchange)
Is it likely to get punted (or drift) - If so then that changes where i'd bet.
EW terms or the place markets