Oh, I am empathize with you. Yes, in the summer, it can be very problematic to "hide" the straps of a neck-style wallet, especially when it is so hot that the extra layer of even a light scarf can add extra heat. But, that's the only solution I've found....to add just add just the lightest, airiest (sp?) scarf tied a little lower around my neck to hide the big squarish, stiff bulge that results when one wears a neck wallet. And, the thinner one is, the more that big, still bulge stands out. And, it is stands out, that defeats the whole purpose of hiding where one stashes their stuff, right?
The waist wallet also causes that bulge to appear, just in a different place.
And, while some will say you should not have to access the items you have inyour safe neck/waist wallet while out and about, I have found at times that I DO have to access things while out and about....the unexpected large purchase or needing to show an ID (where we did not think we'd have to), etc. Yes, you can always pop into a restroom to pull out what you need to pull out, but I prefer just turning (in a private corner) to pull out my neck wallet, etc. vs. having to potentially get up under a dress to access it.
There have been a few times that I have worn a neck wallet turned around, so the bulge part would be actually on my lower back (but that can cause issues in crowded trains or just crowds in general.
I've found a preference for traveling in shoulder season, just so it is easier to add that extra scarf to hide the neck wallet. But, that said, yes, I would still jump at the chance to go on a special middle-of-the-summer trip, I'd just add a light scarf to hide the straps of the neck wallet and have the scarf tied such that it hides that sure-to-happen bulge. A light gauzy white over-shirt could also work (and provide just a smidge of protection from the sun, too).
Then, I added to the problem when we renewed our passports last time, and we requested the passport version with more pages (since we filled out normal size passport so quickly). Gosh, that thicker passport (I exaggerate) feels like one is carrying the NYC phone book around her neck!! But, not exaggerating, it really is significantly thicker and stiffer than a typical passport..........so neck or waist wallet, it requires some sort of extra fluffy cover to hide the bulge.
My sister sews in special zipped pockets into her clothing, and I guess that could work better in certain circumstances.
For our larger supply of emergency cash, the extra credit card, emergency phone numbers, etc., I've altered a neck wallet that my husband wears holster style under his arm. Does it get wet from sweat during the hot summer? Oh, yes. We save specific sized plastic bags for extra protection. We also take an extra one altered neck wallet for him to wear while the other dries out.....yes, ewww, gross, but it works. A woman could also wear this in a similar fashion, and that would leave just one strap to hide around the neck, and I guess you could fashion a temporary velcro or other loop to pull it under the shoulder seam???