In general, yes, but there are a number of other variables here that may impact how much effort you put into it.
Who is the audience?
If it's "just a couple of engineers," quick-n-dirty may be just fine, and in fact preferable. Get it done and move on. If it's for more than a couple people, or for people in different groups, then spend a little more time on it.
How often will it be used?
This might be the most important question. If it is going to be used often, a good design will be not only appreciated, but the extra efficiency of your users will make up for any extra time spent on the design. I have used apps in the past where even simple things like Tab Order weren't taken into consideration, which made data entry a real pain.
How long will it be used?
This may be a little more difficult to predict, but in my experience, it will be used more often and for a longer period than you first anticipate, and may even evolve and be repurposed over time. A little thought ahead of time may make this transition easier.
Will it always be internal?
Again, based on experience, if the right "internal app" gets into the right users' hands, it could eventually be added to the "real" product suite. I've seen it happen numerous times.
Good design should usually be a general practice, and practice makes perfect
It's occassionally fine to "slap something together," but as a developer, I find that if I apply my general principles and coding style to almost anything I create, it becomes that much easier to do. The time it takes to create a good design will decrease as you get more experience, and you will become a better developer for it.