NickE,
I feel for you, I have been in similar situations. May I offer from my own experience:
Remember that your purpose at the company is to provide your experience, information, skills to benefit the company goals. Companys have no obligation to use your ideas (public safety concerns aside). It will help your career to present your opinions in a manner that is as easy as possible for your peers and higher ups, and preferably in a way that is perceived as helping the process.
First, when I have difficult situations, the most important thing is to take an emotional step back. The exchange of ideas shouldn't be personal - though it is very easy to take it as personal, especially when there are personality or cultural clashes. Here it is very helpful to have a friendly relationship with your coworkers. I LOVE smacking down people that I can't stand, and rush to defend people that I like - its human nature, not very professional and bad for the process, but will never change. Maybe
NickE can get over it, but I guarantee your coworkers won't. Surely you can find a few things of interest to discuss with coworkers. Go ahead and be inefficient and waste a few minutes by the coffee pot talking, join a group lunch a few times a month, invite some people over to your place to watch the world cup, or enter the office basketball pool (if you don't know anything about sports - talk to the office guru for tips - it'll flatter them to no end). It's not wrong to "waste" company time doing some of these things for the sake of team building.
Second, try to start your differeing opinions from areas that you have common agreement on. Then present your opinions as ways to meet the goal or build on success. EG, Agree that Bob's suggestions make the widget cheaper to produce, and express that you will also reanalyze the failure scenarios to ensure there won't be a detrimental effect on product life. Notice you don't have to say that his suggestion is good or the best, just that it does help in someway. Then you will simply do the required work to help document that the changes won't affect other areas - even if you strongly suggest that they will.
Third, explain your progress to your boss before presenting to the group and let your boss present positives and negatives. A wonderul boss will take heat for any percieved negativism and let you take the credit for solving the problem. A good boss will simply back you and stand firm to your results. If you do the presenting, be simple and clear, don't speak down to marketing and don't try to sound like you have a master's degree in engineering because it won't impress anyone. Allow the group to go into detail as necessary and expect some criticism. If the suggestion ends up making a huge financial benefit, it will probably outweight your concerns. That's life in corporate.
Finally, sometimes go with what others want and don't be a jerk, this shows trust. This is especially true when working for people who are under you on the corporate sturcture, and when the outcome is NOT going to be disasterous to your time line or budget. Don't be patronizing, maybe others just need the opportunity to learn through their own experience what you already know. Maybe you will learn something, if nothing else it helps to add to the knowledge base.
I hope these suggestions help you. It sounds like you have lots of time left in the working world and the sooner you learn to work within the corporate bounds, the easier your life will be.