My understanding is that we have cluster mailboxes for safety reasons due to the large number of people with dogs. It also cuts down on the amount of time it takes the mail carriers to deliver the mail.
As for safe areas near I-70 - you might want to look in High Range, Sagecrest (both off of Roadrunner Pkwy), Las Alturas and maybe one of the areas off of Foothills (Scenic Drive) or off of Telshor (Majestic, Arrowhead, etc.) The houses are older than those in Sonoma Ranch and tend to have larger properties. The one downside is that many have not been updated, so it is a bit of a trade-off. There are a couple for sale on Santo Domingo and one on Frontier Drive (Sagecrest) in your price range. There is also (at least) one on Cheyenne Drive, one on Stage Coach and one on Cloudcroft Circle (High Range). High Range, Sagecrest and Las Alturas put you in the Desert Hills elementary and Camino Real middle school district.
There are also some nice older houses near Kohl's off of Triviz (Loma Heights), but I am not as familiar with that area, you might also consider the area with the streets with the planet names (Mars, Venus, Jupiter, etc.) That is close to I-70 as well. Again, these are older areas (mid 1960s-1970s) so the houses probably need updating, but, prices are lower and you definitely get more property for your money than you would in Sonoma Ranch.
Here are a couple of links to houses in High Range and Sagecrest:
2200 Santo Domingo Avenue, Las Cruces NM - Trulia
2823 Cloudcroft Circle, Las Cruces NM - Trulia