1999 Toyota 4Runner starter, ignition or alternator?

Dear Andy
From the information you provided I don't think it is the alternator. If it was then the battery would eventually go dead and the car would not start at all. Your neighbor could be right but, like you I hate to change parts without any reason or cause. I would first check the battery cable connections. More often then not this is the cause. Make sure they are clean and tight. If this isn't the problem then have the battery load tested. ( I don't know if temperature is a factor for not starting) You can get it done for free at some of the big chain stores like Sears, auto zone etc. If this is good then when the car fails to start check that power is getting to the starter. This will eliminate the ignition switch, relays and the wiring to the starter. You can use a voltmeter or 12volt test lamp to make the test. If there is power then the starter is bad and needs to be replaced. To confirm this, those same stores will bench test the starter for you for free. Good luck :)

You need to get batttery tested, starter draw tested, altenator and regulator tested, all at once and repair or replace whatever's bad, all at once, each item can cause the other items to go bad in a short time.