Lesley,
I lived for four years (11/95-11/99) in the middle class portion of a well-known "middle to upper class neighborhood" in Santo Domingo, and we never needed a security guard. We were robbed once, but it was clearly an "inside job," something a guard would not have helped against. [One consideration for you: Dominicans frequently say that robbers are tipped off about best times and where to find the goods by house guards!] There were houses in our neighborhood (but not near us) that had guards, but they were all well-known politicians, diplomats or the very rich, all with houses 2-5 times bigger than ours, and so clearly needed one. The rent you cite is actually very high by Santo Domingo standards, so perhaps your house is correspondingly huge and thus would warrant special protection. If by chance you are renting a condo in one of the many luxury "towers" that have sprung up in Santo Domingo in recent years, I do not think your own guard is necessary -- these towers all have their own security.
I would suggest waiting until you arrive and check out the situation first. Make some inquiries of the neighbors, see what others are doing. If your home does not appear so lavish from the street, if you have the privacy of high walls, and if you exercise the type of caution that you would in any large East Coast US city (most importantly, don't flaunt and don't discuss -- with ANYBODY -- what you do and don't have at home), then a guard is not necessary. A large dog might be a good idea, and certainly new locks on the main doors (no telling how many maids had a copy of the key before you moved in!).
As for walking down the street, I did it daily for four years without problem, and there is no way anyone would mistake me for a Dominican born-and-raised. My kids and I went to Mirador Sur park frequently throughout the week. And several times I walked 2-3 miles alone in the city. But then, I was wearing simple clothing, no jewelry, always act like I know where I'm headed (even when I don't), speak fluent Spanish stuck to neighborhoods I know not to be high risk. Just as in any big city anywhere in the world (at least all the ones I know, and they are many), if you are "advertising" yourself as a worthwhile target, a mugger will pick you over a less obvious target.
I would suggest spending your first couple of weeks having various folks take you to different parts of the city you'll probably be frequenting in your daily life, and give you a chance to scope out which ones are riskier than others.
People will also tell you to put an alarm on your motor vehicle. Everyone seems to have one. But in truth I didn't use mine for the last 3 years of my stay in SD and my car was never bothered. For that matter, nor were any of the cars of my friends and family. I did use a Club, but that only deters those wishing to steal the whole vehicle. If you drive a Mercedes or BMW or Lexxus, okay, then get an alarm. But if it's a Honda or Toyota (wiser choices in light of the cost of fuel in the DR), then don't worry about it.
Please take all the dire warnings you'll hear with a grain of salt. I too heard them all from my Dominican family and friends before we moved there, and most of them turned out to be very inflated. Take sensible precautions, but otherwise please relax a bit. Santo Domingo is hardly the security risk that New York City (I lived there for 3 years too) or Rio or Sao Paulo are (I visit them often),and in fact is by comparison quite safe. Many Dominicans living there think that it's not because crime is much worse than before, when it was minimal. It's all relative, isn't it?
Hope this helps.
Regards,
Keith