Good post that brings up some interesting points. I think the real emphasis for us is empowering the journalists in the whole process. If you distribute press releases through a variety of communication channels journalists have the option of selecting which ones are most suitable for them and this should result in more engagement from them (which is the whole point after all). As Twitter is so popular with the journalism community it seems a natural choice.

Given the rapid advancement of online communication we should be moving away from mass distribution systems like email lists and towards smaller, far more targeted distribution. Muck Rack and MicroPR are good examples of people using some creative thinking to get the right information to the right people using the online tools available. As you say, you are unlikely to get huge quantities of clicks from Twitter for press releases but the people clicking through have made an active choice to receive the tweets so are more likely to engage with the content when they click through.