The question I would ask is why are you upgrading?
Is it that you have run out of things you can see with the 8"? (unlikely)
Is it that you just want a bigger scope? (we all get that fever)
Eyepieces can make a huge difference in how things look and your ability to get the right magnification to get the most out of things. You only have the two original eyepieces and that is what you have used for years.
Having only a 30 mm and a 9 mm is just too limiting for that scope. Eyepieces don't go bad and you can keep them when you sell the scope. So anything you add will transfer to a new scope later. My leaning would be to add eyepieces and or the Barlow as you suggested. I would not replace current eyepieces, I would fill in to extend what your current scope can do. You have a 30 and a 9. So something in the 15-20mm range or a zoom in the 7-21 or 8-24 range.
Many people feel 2" barlows are not a worthwhile tool. They are large and heavy and people say that 2" eyepieces are only for low power wide views. I say, why not get double use out of them.
I like my 2X 2" GSO barlow. I have two 2" eyepieces and I sometimes barlow them to take advantage of their wide view. My 38 and 25 mm 2" eyepieces also give me 19 mm and 12.5 mm so I don't have 1.25" fixed FL eyepieces in that range on this scope. It is heavy so it may throw of your scope balance a bit but just adding a bit of counter weight to the bottom of the scope addresses that if you need it. I have not found the need.
http://agenaastro.com/gso-2-2x-ed-barlow-lens.html
My most used eyepiece is an 8-24 Zoom. This is usually the first eyepiece to go into the scope.
http://agenaastro.com/celestron-8-24...-eyepiece.html
Or you can add somethign in the midrange in a fixed FL eyepiece. Maybe in the 14 to 20 mm range. If you add the barlow be sure to take that into account when you pick. Your 30 becomes 15. So maybe a 12.
http://agenaastro.com/eyepieces/1-25...tml?price=-100
A wider view eyepiece for those large items or as a next step from your finder scope. I use mine for both. I have the Agenda Astro 38 mm 70 degree. And I barlow it to 19 mm.
http://agenaastro.com/agena-38mm-sup...-eyepiece.html
A barlow would take your 9 to 4.5 mm so you go up in mag at that end. It all depends on you, your budget and your goals. But with only 2 eyepieces your current scope has a lot more room to grow.
Portability
A 12" will pull in 2.25 times more light. Nothing to sneeze at. Are you suffering from lack of light gathering? Certainly 12" is better than 8 from that point of view.
Is a 12" too inconvenient to move about? Only you can judge that. When I bought my 8" I was also considering a 10" which was 15 pounds heavier. I could have managed it but felt the lighter, more portable scope would get more use because it was easier to handle. I am happy with my decision.
One way to address portability is a cart. My scope lives in the garage on a cart. As I am moving it down the driveway and along the sidewalk this one works well for me. If I was going over rough ground, perhaps a hand cart with an extended platform attached. Easy to slip the scope off the cart and back on when done.