What is the point of money if you can't spend it/exchange it? Nobody will want to use your currency if it has been horded by miners since day one. That will mean terrible distribution and miner top heavy control of the currency and nobody can trust it. Exchanges are the single best promotional tool that coins have. If they are not worth money, how can they be expected to be money?
I just don't understand what the fear is here. That people will pump and dump and it will be forgotten? If you actually believe in the fundamentals of this coin (which it clearly has to all of the people who understand the power of the technology) then pump and dumps are irrelevant. Fundamental advancements like wallet releases, etc. will make the coin grow in the long run regardless of what the market decides to do with the coin. By putting the coin on the biggest exchange such as Mintpal, you are creating trust in the coin over time and brand awareness. This is critical to the public's trust in the coin and it having a fair distribution through liquidity and market fluctuations. I think it's misguided to think that you can just hide in a corner for months and then burst on the scene. You would do a disservice to the technology because it will be atrophied and take much longer to gain acceptance and usage.
Finally, the biggest problem that I see with the plan (or lack thereof) of not putting this coin on more exchanges, is that in the 3-4 months time window you guys are shooting for with the wallet release is that you will potentially be competing with Zerocash. From what I understand I feel that ring signatures are more trustless than Zerocash because of the possible exploits of Zerocash (not being able to detect if someone secretly increases the total coins, requiring trust in the developers in the opening ceremony, newer untested cryptography). But still, do you really want to compete head to head when you could have had months head start to convince people that your technology is superior? If public opinion turns against your coin or it is forgotten, then what is the point of all the work you did?