I've lived in Plainfield for 17 years - previously lived in Queens, NY. I used to live not far from the location you mentioned - lived on Pemberton Ave off of Grant, I now live close to Muhlenberg Hospital. Plainfield has its problems like anywhere else, but overall its's a nice town. It has great housing. The downtown needs a better selection of stores. There's nothing wrong with 7th & Grant Avenue but you should drive through the entire town before you make your final decision. Drive down Grant, Stelle, Sherman, Plainfield Ave, Woodland Ave, Kensington, Watchung, Leyland, the Eastside of 7th. Pemberton Ave thru Cedarbrook Park, any of the streets off Kensington or Woodland. They should give you some idea of what the town looks like. Quite often the people who complain the most about Plainfield don't live in Plainfield. If your children are of school age, the schools are okay up to middle school, but parents who can afford it send their kids to Union Catholic High in Scotch Plains or Bishop Ahr in Edison. Many times I've walked past homes or cars with their doors and windows open and no one breaks into them. There are 2 Plainfields - the small part where the bad things happen and the majority of the town that is nice and safe.
Good luck with your decision.