Like they say in fly fishing "match the hatch". The level of design effort and presentation quality has to match the project, client, and investment that you or your client are willing to make.
I'm a Registered Landscape Architect with very poor hand drawing skills. That is one of many reasons that I draw in CAD. You still have to apply the same drafting principles in CAD and you still need to learn about the tools that you are drawing with. That's another subject. Back to "match the hatch".
Papercutter is right on the money in his understanding of the landscape design business. It is very diverse both in what a client needs as a design, what the range of complication and graphic presentation is necessary, what an individual's skill sets are to do it, what direct competitors are doing, and what is economically efficient to either sell or invest your time in doing.
The first rule is to get the most out of the skills that you have and do not force yourself to work beyond your capabilities. If you are not a master of color renderings, work with black and white line drawings. Not even 5% of my plans have seen any color. Part of it is that I'm not great at it, but most of it is that it adds to expense and it is easier to sell cheaper plans than more expensive plans.
A design/build contractor is making a plan in order to communicate what will be built in order to get a contract. That is a lot smaller a task than developing a plan to go out to bid for multiple contractors to make apples to apples bid proposals. In other words, it should be simple in terms of technical information with an emphasis on selling them on the end result.
Make no mistake, the best selling that you can do does not have to be through your graphics, but through your ability to describe the landscape that you are proposing. The strongest way, in my opinion, is to describe why each piece is laid out where it is - how it affects the appearance of the house, how it distracts attention from the driveway, how it screens the neighbors RV, how it frames the view of the lake, how it makes the front door the center of attention from the street, .... I do all that the first time I meet with a client (for free) and then get them to hire me to draw a plan for $1,500.
It is just an easy to sell a $7,000 foundation planting and walk with a minimal sketch. Those folks want to spend their money on the walk and shrubs, they don't care about hanging a plan in the living room. You can laugh and say "my craft is building landscapes, but here is a rough idea of the layout that I'll do for this contract".
I have other LAs (on message boards) telling me that you can't be successful without doing 3d fly throughs and using the latest and greatest software and graphics, but they are looking for jobs and I'm making a good living in a bad economy doing very little more than just selling 24x36 pieces of paper.