If you very specifically want to do mechanical engineering specializing in mechanical engineering design, I would _HIGHLY_ recommend make plans on going to grad school.
The reason I say that is this:
I had the same exact idea, and this was the reason I got my ME degree. However, unless you graduate in the top %10 of your class, you're going to be severly limited in the number of offers you get for mechanical-related design jobs. The semester I graduated we had 154 companies come recruit at the College of Engineering career fair ... the guys I knew who graduated with 3.2+ GPA's more or less got the job offers they wanted, the rest of us kinda had to take what's left over. The other issue with this is, the type of jobs that a person with a 4-year ME degree would have done as an engineer 20,30 years ago have all but completley been replaced by computer software ...
However, if design is what you surley want to do, I would definatley make plans on going to grad school as you will have a much better chance at landing a good design job.
The thing about mechanical engineering is that it's so broad, you get done with it and it's like you know a little bit about everything, but you don't know very much more than that. If you go to grad school, you specialize in a specific area of mechanical engineering, be it statics (structural design mainly), dynamics (dynamic control, vibration analysis, etc), or thermo and fluid dynamics ... over the course of your 4 years, you will kinda figure out which area is most interesting to you and which one you are best at. For me it was always the thermal fluids stuff.
Again, if you specifically want a design job and don't wanna do HVAC work, make sure you have a high GPA ... that's really your only recourse.
Outside of that, if you look at the average starting salaries for all engineering disciplines, the ChemE's start out at roughly $5,000 a year more on average than the ME's and EE's do.
If you aren't going to be dedicated enough to pull a high GPA in Mechanical Engineering, I honestly would recommend getting a Chemical Engineering degree. It's generally regarded as a more technically difficult degree to get, and short of the control theory, vibration analysis, and perhaps the design classes (which IMO you don't really learn that much from in undergrad anyways) you basically take all the same stuff, except you take more thermo in ChemE school.
If I had it to do over again, I would have gotten a ChemE degree.
I still haven't ruled out the possiblity of going to grad school myself, it's just affording it right now that is the problem. See, I went sledding a lot last winter. Hahah
Anyways, I would think about it, but if you aren't ever planning on going to grad school, I'd look hard at what kind of job offers ChemE's or PE's are getting. You get a PE degree you're virtualy gaurenteed an $80,000 USD a year job right outta college. Only problem with PE degrees are, you have to go where the work is, which may be Yemen, Iraq, etc ... ChemE you would theoretically have more options.
I dunno, ME was a good degree to get, I just wish I would have studied harder and pulled a higher GPA to get the job offers I
really wanted instead of getting stuck with a ****ty *** job working for an oilfield service company.