Lerner has already pumped around £140 million into Villa since he took control three-and-a-half years ago.
Mortimer told the Sunday Mercury: "There's a lot of optimism for not only this season but next season because, no matter what happens this season, they'll need to build on it and strengthen the squad.
"It's quite interesting reading how much Villa have spent this season. They've done it in a way where some players have gone under the radar, but when you add it all up, they are actually one of the highest spenders. So, from that point of view, they've been quiet with putting their hands in their pocket.
"The end of the season will be the dictator about how it has all gone. It's all well and good getting to a final, a semi-final and finishing in a top six place again but that's only really the same as last year and the year before.
"The questions will be asked again as to whether they can go that extra inch and get the extra players that they know they need to finally turn it around and win a trophy or two.
"That is the question that Martin O'Neill will be asking of his staff and also of Randy Lerner - because he's the man that will fund it all."