Stein is usually very thorough in his planning, so I may be missing something with his thinking, but I don't think the slip switch is essential to the yard in your situation. If you replaced it with a simple turnout (like the RH one that comes off the main right there by the slip) you could still access the ladder from the lead.
I'm not certain, but the slip may simply enable the yard to have separate arrival and departure tracks, which on your layout would be overkill. Slip switches are expensive too.
The purpose of the double slip, as originally drawn, was to allow inbound trains (which would be coming from the left only for the layout the track plan was drawn for) to go into any track, to avoid having a single A/D track being a bottleneck for all arriving and departing trains.
This is a yard that was intended for relatively frequent termination and origination of trains, and building several trains at the same time.
Might be a bit overkill for just supporting local switching.
For a look at a cool local yard for a switching layout, have a look e.g. at Bill Kaufmann's State Belt Railroad from San Francisco in these videos:
http://convozine.com/conversations/7989
If you look at about the first three minutes of the uppermost video, you will he the main yard for his layout - the King Street layout - it is located in the lower right hand corner of his track plan here:
http://statebelt.org/layout/thumbs/newestbeltlarge.jpg
Basically two-three parallel tracks that could hold maybe 20 cars or so while things were being sorted out.
A yard doesn't have to be all that big to work just fine for supporting some local switching.
Have a look at "the patch" Keith Jordan's amazingly small L shaped layout consisting of two 8 foot long shelves - one 12" deep and one 10" deep, wrapped around an outside corner in the 2011 Model Railroad Planning magazine.
Mmm - found a web page - you can read more about Keith's layout here:
http://web.mac.com/ckjordan/The_Patch/Patch_Home.html
The track plan is on this page:
http://web.mac.com/ckjordan/The_Patch/Layout_Plan.html
There are several urban smallish yards on this track plan suggestion which I drew for someone in a different forum quite a while ago - one along the left wall, a smaller one along the right wall and a third two track yard on the left side of the peninsula:
The small three track double ended yard along the right wall is based on the track plan for the main yard on Nick Kallis former E-shaped urban layout from New York City - that tiny little yard originated like 4 or 5 local turns during an operating session - one train going to the float yard to pick up cars, one serving the freight hours, one serving the peninsula and and so on and so forth.
Here is a a couple of small yards on my interpretation of Thomas Garbelotti (Scarpia in various MR forums)'s Vermont inspired layout, which he is building on sectional shelves balanced on top of IKEA furniture in a small 22nd story apartment in Abu Dhabi in the Persian Gulf, where he is currently teaching.
The track plan design is by model railroad designer Byron Henderson - you can see pics of the layout build at Joe Fugate's Model Railroad Hobbyist Magazine ezine website:
http://www.model-railroad-hobbyist.com
Basically, it comes down to how you plan to use the yard.
Small auxiliary yards of all kinds (both urban and in small town yards) can be built surprisingly compact, if their main purpose is to help serve local industries, rather than being efficient routing machines (which is what bigger classification yards are supposed to be).
Smile,
Stein