It's *not* hard....at all. It *is* time consuming - because I remove the wiper cowl and intake plenum. It's *not* something you need to pay someone else to do - as long as you can read your service manual, not difficult at all. *DO* be careful with the vacuum lines as you mark and remove them - they are very brittle. Ideally, you'll have at least all day to dedicate to this task.
IMO, removing the intake plenum is wise because it gives you a chance to inspect the valve covers - all the bolts on my rear valve covers were way loose, and probably the real reason it was leaking, but I went ahead and replaced the valve cover gaskets as well. Many folks complain that removing the wiper cowl and intake plenum are too much work - but it makes access a breeze and you can actually torque the spark plugs properly when you re-install them. And you can easily check the torque on those rear valve covers.
I'd far rather spend my time removing a few extra pieces than waste a lot of time trying to get that perfect angle while reaching up in a cramped space with less-than-ideal leverage.
2003 Honda Odyssey EXL (3.5L)
1997 Town & Country LXi (3.8L)
1992 Honda Accord LX (2.2L)
1990 Chevy K2500 (5.7L TBI)