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I think the more important question is: Why are you interested in urban design programs? What is your background (architecture, urban planning, etc) and what is the highest degree you've obtained or are currently working on? There are some tough issues associated with wanting to obtain an urban design graduate degree and its potential, or lack thereof, for your future career prospects. Tell me your answers to those questions above and I'll try to give you insight and maybe I'll convice you to get your MLA instead.
If you are willing to spend or go into debt for $25k to $45k, then yeah, go for the MUD degree. Unfortunately, you will find that having both an MUP & MUD will not grant you any special privelages when it comes time to interview for a job. If a firm, assuming you want to jump into the private sector, wants some one to produce gorgeous renderings of a site for a client, they will almost always go with some one with an architecture background. They have the studio time and experience that a one-year/two-semester MUD program cannot deliver. However, if you are not expecting any extra salary for the MUD training and are willing to start out at a planning firm on the same level as some one with just an MUP, then you should probably consider the MUD. But the $25k to $45 is a big chunk of change and you should spend it wisely. Consider this strategy: Get your MUP, work for about two years at a consulting firm, learn how designers are utilized at the firm, and then chart your course. Those two years will tell you everything you will need, and while you're making money, you will see the real value of an MUD and an MArch degree.
But if you want to stay in school at this time, then make the shift to a Landscape Architecture program. Many of your MUP credits overlap with MLA degree programs, and you can cut your time in the MLA program down from 3 years to 2 years. Why do I advocate an MLA degree over an MUP degree? Prestige and greater job opportunities. With an MLA degree and an MUP degree, your future employer will be able to market their talent to potential clients, and having some one on staff with an urban and environmental background will make their ability to score more projects much easier. Many projects require landscaping details, and with the MUP, you have the concepts and theory down pat, but the additional MUD is lacking in the sense that your studio background and environmental knowledge will be limited. The MLA degree makes up for those two deficiencies.
But don't take my word for it. E-mail some professors from both MUD and MLA programs and hear what they have to say. But watch out, they all will say that their program is great, you should come here, etc, etc. Because you are not yet a tuition paying student, they will give you all gloss and hardly any of the downsides.
Ultimately, you are going to compete for jobs against people who have the archtitecture background. My first studio professor when I was an MUP student encouraged many of his students to consider the urban design program at the University of Michigan (http://www.tcaup.umich.edu/ud/). I gave his words much thought, and the following year when I was his TA, I asked him about the career prospects in urban design with a dual MUP & MUD background. He told me bluntly that I would need an architecture background to deal with real urban design. Of course, he also told me not to discount urban design as a career - an MUP is valuable in the sense that I can help communities draft urban desgn guidelines. If you love policy, then stick with the MUP. But if you want to do the real sketching/rendering/drafting/CAD, then you need more than an MUD.