Why would he rather spend more money on leads.....? If it's because you're already maximizing your opportunities and you have a 15-20+% closing ratio on your existing leads AND you have the staff to handle more leads, then you may want to consider adding. But let's agree this is usually NOT the case.
I would consider a tool that will allow you to increase the performance by getting your show rate up on existing leads. Both Hooklogic and Conversica can help with this but do take a different approach.
Conversica - lead nurturing using timed triggered / responsive follow-up emails. It's like having a dedicated BDC specialist sending out quick follow-up emails. Especially great for those leads/customer higher in the purchase funnel.
HookLogic / AutoHook - Increase your lead to show rate by double or more by incentivizing high intent customers (by GEO, vehicle of interested, inventory, etc.) to get their butts into your dealership. You can also use these incentives within your emails, phone calls, Print, Direct Mail, BDC, Chat - etc.
HookLogic Wed2Show will ALSO gain you more leads by increasing conversion on your own dealership website, landing pages - traditional and mobile.
Again, two very different products really. I've seem some great success when you work HookLogic and Conversica together.