We were in Slovenia last September and hiking is our jam. Here are a few suggestions:
1) Everyone has heard of Julija, and the food is indeed excellent. When we had dinner it was packed with noisy Americans and the waiter was a bit indifferent. We very much enjoyed Gostilnica 5-6 kg (recommended by leeshao on the forum) and enjoyed it so much for lunch we went back another day for dinner. Great pizza but also great entrees and salads. I had a wonderful sea bass. Fun wait staff. And it will give you a little walk from the center. It could be worth it to see if you can get into Julija for dessert. Our favorite out of the way restaurant was Azur Tratorija. A real long walk or a short drive from town with parking.
2) Something I have not seen mentioned in the Skocjan vs Postonja cave debate is the quality of the return hike at the end of Skocjan. The long return hike takes about 2 hours and on it's own is worth double the price of admission. Every corner you turn you come face to face with another jaw-dropping spectacle. (I have not been to Postonja, but we loved Slovenia so much we are returning next month, and plan to give Postonja a try. We are also thinking about finding the return hike at Skocjan and doing it as an out and back.)
3) The Vintgar hike with the circuit of Lake Bled is probably enough, though you could also consider hiking up from the island end of the lake (near to the crew boats) for the marquee view of Bled. It's steep but worth it.
4) Bohinj was our disaster location. No Cow's Ball and our lodging was so horrible we had to switch. We didn't go up to Vogel as it would have eaten up a lot of the day for us. But the hike to Slap Savica is quick and easy, and hiking a bit around Bohinj is also nice.
5) Personally I would put a loop over the Julian Alps above a day at Bohinj sans Cow Ball. The drive is amazing and you can make a lot of stops or not. I guess you could also just take the Motorail from Bohinska Bistrica to the Kobarid area. One of my favorite hikes was a silly little thing right off the road through a magical forest to Slap Boka, not far from Bovec. The stretch of Kobarid's historical trail from the Napoleon Bridge to Slap Kozjac is also a winner, and not too long. We remember that fondly as our rafting and two waterfalls day. You just don't want to miss the Soča River. We are going back for more.
Have a wonderful sampler tour. I hope it leaves you dreaming about "next time!"
Ann