Had I been working at NASA in 1969 I would have looked forward to the landing on the moon--well planned out, ready to go, made sense. (Always loved aviation and aerospace and would later get my pilots license.)
I went to Auto Europe and could not find a 41 pound rental rate. But since we don't know the dates Dave is traveling, it's irrelevant.
Roger, if you like driving around cities in the middle of the night, more power to you. I'd prefer making a trip during a time I can spend time there and really see it. It's not about risk taking or being adventurous--it's about getting the most out of that adventure.
And to use your insult as an example. If Dave followed your advice and rented a car, it would be like all he did was "circle the moon." Planning his next trip to include London would be like "landing on the moon." Perhaps you feel circling is better than nothing. I'd prefer to return and land on it.
I doubt this will be Dave's last trip to Europe. As Rick Steves, and most of us here say, "Plan to go back."