I'm going to suggest that the 17-40mm focal lenght range is rather difficult to learn on, and is also an immensely boring and dreary range of focal lengths on a 1.6x crop body camera. The 17-40 translates to 27.2mm to 64mm in 24x36mm focal lengths, which offers semi-wide angle to the "dead zone" of 55 to 64mm which is a sort of no-man's land that has proven to be an exceedingly unpopular focal length for literally,decades. The list of failed 55 and 58mm lenses is long, and shallow. Pentax, Nikon, Mamiya,Topcon, Pentacon, and a few others have made 55 and 58mm lenses, and the acceptance of them by the public has been exceptionally tepid--even when those lenses were super high quality, ultra-speed offerings like f/1.2 or f/1.4...people simply do not want, or buy, lenses that offer the over-50mm but under 70mm focal length or equivalent angle of view, and they have made virtually ever offering a commercial dead-end. Since the 1950's.
So, yes, definitely, consider the 18-200mm lens as one that offers a HUGE range of pictorial options, in a single lens that you do not need to change. The optical quality of the 18-200mm lens might not be super-fantastic, but the **pictorial** potential of the 18-200mm lenses is huge. You asked for advice, so my advice is, keep the 17-40-L as a high-quality lens with limited range only if high optical quality is a concern to you. There's a difference between getting the shot you WANT to get, and getting what a lens is able to get, but being dissatisfied with the results on a consistent basis. As a newcomer to photography, you would probably find your way more readily if you had a lens that was not so constricting and so limited in its range of focal lengths; you have absolutely NO telephoto capability with the 17-40...it offers absolutely zero ability to compress distance, and zero ability to offer narrow-angle compositions. There are numerous 18-105,18-135,18-200mm zoom lenses currently on the market from six or seven manufacturers, and they are very popular lenses with hobbyists and for people who want versatility and adaptability; the 18-XXXmm zoom lens is know as a walkabout or travel or all-in-one or superzoom lens, and it has its place. If you bought one, you would be in the company of millions of other owners.