Before I go any further, I'd say that I'm a little bit concerned about the question chosen to capture people's voting intention. You would have been better off providing actual parties (or something generic like "extreme right wing party", "moderate right wing", etc.) rather than providing a 10 point scale question. The reasoning is that people who vote for extremist parties tend to have more in common than those who vote for moderate/centrist parties, whether it is on the right or on the left. But by using a scaled variable, you are assuming that their decisions are linear in nature down the left/right political spectrum.

Moreover, since people can interpret scale points differently from each other and from you, you end up categorizing people in ways that may not be reflective of their actual voting intentions. For example, if you choose between 3 and 4 as the line drawn between extremist and moderate right wing, it's possible that a respondent considers 3 to still be moderate right wing. You'd thus mis-categorize that respondent.

I'm not familiar with running MNL on SPSS (I use R when I do this), but you should end up with 4 different models (# of categories in the DV - 1). The 1st category is typically the one omitted (so in your case, "extreme right").

The easiest way to interpret the output is to apply the logit rule to get the probability of voting for one party over another, given the specific IVs you included in the model.

First, you need to calculate a certain situation - so pick a certain value to give to each IV. Then for each of the 4 models, multiply the IV's values you chose with their B coefficients, and their constant. You will end up with a score for each of the 4 categories. The omitted category is always given a score of 1.

Second, apply the following equation to each result to turn it into probabilities:

For the first omitted category: 1/(1+exp(scorecat2)+exp(scorecat3)+exp(scorecat4)+exp(scorecat5))

For each of the other 4 categories:

Exp(scorecat2)/(1+exp(scorecat2)+exp(scorecat3)+exp(scorecat4)+exp(scorecat5))

Exp(scorecat3)/(1+exp(scorecat2)+exp(scorecat3)+exp(scorecat4)+exp(scorecat5))

Exp(scorecat4)/(1+exp(scorecat2)+exp(scorecat3)+exp(scorecat4)+exp(scorecat5))

Exp(scorecat5)/(1+exp(scorecat2)+exp(scorecat3)+exp(scorecat4)+exp(scorecat5))

You should end up with a percentage for each of the 5 that adds up to 100%. Those are the probabilities of someone's voting intentions given the IVs you specified.

Try it again using a different value for their income, and observe the change in probabilities. This should provide you with an indication of what kind of impact that particular variable has on their voting intentions.