Sadly it won't make a difference. The GOP electorate is much different than I imagined.
I hope that it is not too little too late as well. Nevertheless, I am happy he made that speech. One of the problems with the GOP primary so far has been that all candidates' ideas (especially on the economy) were treated as equal merit, without enough critical thought. There never was any serious discussion whether the VAT scheme, proposed by Cruz, could sink the economy or if Trump's illusive attempts to find savings would ultimately result in canning some useful budgetary spending. Instead, silly arguments about "no experience" being better than experience, stigmatizing a whole religion and of deporting millions of people were constantly floated around as credible policy choices.
As a result of this vacuum of serious policy and economic thought, most primary voters are treating this GOP contest as a Beauty Peagant - choosing the candidate who sounds the best or whose morals they identify with most. The problem is that the voters are implicitly assuming that all the candidates would do an equal job, once in office. They simply shouldn't assume that and there needs to be critical analysis on the economic impacts of some of the proposed policies!