I have Skyrim for both Xbox and recently PC, the reason I changed to the PC version is that the Xbox version is, for all intents and purposes unplayable on my box. Every update screws it up that little bit more, I can't play a session now without it crashing or freezing two or three times.

With that said I've decided to wait until Dawnguard is out for the PC before obtaining it. Could someone give a little advice here? Is it better to start a new game to play it? What I mean is in terms of difficulty, I'm level 52 with my Stealth Archer character and the game is way too easy, difficulty level doesn't scale wry well with weapon and armour levels in this game, Alduin and the quest leading up to fighting him was way too easy IMHO, and that was using less than maxed out weapons and armour (using standard smithing and enchanted gear, not maxed with potions) and on the hardest difficulty setting.

The dawnguard campaign does throw some situations at you which are kind of tough but by the sounds of your character it won't be too difficult. If your planning on making a new character and doing master difficulty id probly give that a miss may be a bit too hard but your lvl 52 character from the sounds of it should do fine in the dlc.

Well just to start with I am playing on the 360 and aren't experiencing the problems that you have been, like you said yourself it's probably the Xbox that's your problem.

Now I also thought that difficulty would be a problem on my 81 with maxed gear (150mag, 500hp, 450stam base stats) so I stashed ALL of my equipment before starting Dawnguard apart from clothes, an Alik'r hood and two scimitars and tried it out on Adept difficulty. To be fair most of the fights were still quite straightforward with my high amount of health and just took time however there were quite a few moments which were quite challenging to overcome and the expansion was on the whole still enjoyable for me.
My starting class on Skyrim was also a Rogue focusing on stealth and illusion spells with daggers and bows. I completed the Alduin questline at level 14. With this experience I can probably tell you that if you continue into Dawnguard as a Stealth Archer you wont find it very much of a challenge.
You can however decide to avoid using stealth and just rely on your bow in combat which will definetly bring the difficulty back up to par. If not, creating a warrior or a conjuration based mage would probably be another good option as they also get quite a bit out of this expansion.

I hate to sound snarky, but if you try, I am sure you can find a way to make it harder. I agree that stealth archers are a very powerful character type, especially with the perks. But I also know that i could make the game much harder to play, but I don't, simply because after putting in all the hours, I feel entitled as the Dovahkin to be pretty bad.

The Dawnguard - as mentioned - has a few new enemy types, and dragons, and that are tougher. My first encounter with a Legendary Dragon saw my head bitten off.... Haven't seen once since!

My problems with the game on Xbox are totally game patch related, I have the new shape black 250GB machine and 1.6 has screwed everything from popup lighting effects and draw distance to the more important reproducable crashes and freezes with the game.

Thanks all for the input though, I may try Dawnguard with vanilla gear, no buffs to armour or weapons, with my current character to see how it works out. From what I've read it adds about 8 hours gameplay to the game, or 16 if you try both options. I just don't want it to be over before I've had time to enjoy it through breezing through quests because they're too easy. I just wish the game difficulty scaled better to level and gear.