I have a few tents, and I've done them just about any way you can imagine, other than using Permatex. Henry's method is what I now use, with a foam brush, primarily because they're easy, neater and disposable afterward. Be sure to get the odorless version of mineral spirits to do the mix.
Only tent I've ever used a syringe on was the Black Diamond Epic series. I have 2 Lighthouses, a LightSabre bivy and a OneShot. The syringe comes with the tent (or used to), and seam sealer causes the fabric to change color, so there is a wee bit of nervousness involved with doing that one. I did the best I could, but there are some commas and periods on the outside – I say it lends "character". There are times I wish the stuff glowed in the dark – I'd always be able to find my tent.
I used to worry about "looks" – until I did my TT Squall (the old one). Back then, I was worried a lot about proper drying and the potential for having the fabric stick to itself after seam sealing, so I used talcum powder after a short period of drying to "make sure". I put it on a bit early after seam sealing the Squall, and that tent became "The Skunk", 'cause the powder stayed on in a nice white stripe along the ridgeline. Granted, I gave up on the "talcum powder method" afterward: I just let a freshly seam sealed tent set out overnight. After the first few hours, I don't think even a bit of rain would be a big deal.
On Looks: Some 20 or 30 tents later, I figure that, when the rain is pouring down with me inside, the very last thing I'm going to be concerned about is what the tent looks like.