Don't believe all of the hype about buying term and investing the difference (BTAITD). I took a long hard look at the concept and here's a quick summary.
You will be further ahead by using the BTAITD concept during the period when the term premiums are guaranteed.
Due to the nature of the premium structure of level term insurance you will be at a disadvantage when the premium guarantee runs out. You will either have apply for new coverage (assuming you are still healthy) or continue your coverage by paying ever higher and rapidly increasing premiums. You will end up much farther ahead sticking with the VUL concept in this time frame.
I am curious about the face amount of your policy. Do you and your wife have term coverage in addition to the VUL? Is the VUL just on one of you or do you each have them? How did you arrive at the $600k face amount?
For my clients that are in a similar situation, I often use the overfunded VUL concept to supplement retirement savings. It can be a very effective tool. I would never use just VUL to cover a large need, however. As Rich suggested, seek out a financial planner to assist you. The VUL concept is a good one, assuming you need the life insurance, it just may not have been executed effectively for your situation. If it makes sense to do so, you could reduce the face amount of your policy. Premiums on a VUL are flexible within certain guidelines. You could reduce the face amount of the policy, reduce the premiums and still end up with a sizeable account value in retirement.
If you would like me to share more details on my examination of the term vs. VUL concept let me know.