My first visit to Horseshoe Meadows was immediately prior to submitting Whitney. We spent a night acclimating there prior to our hike and it wasn't a bad idea. I grew up at 9,000ft in Colorado, so I hate to admit I have issues with altitude, but I was also a chain smoker back then and I was feeling it on that trip. I haven't been back to Whitney Portal since that trip, but Horseshoe Meadow is in my top 5 spots and I go as often as I can. It's the same climate/ecology as Whitney, but not as steep or crowded. Frankly, if you're not trying to check a box of "tallest thing around" Mt Whitney is probably not worth the hassle.