So what is to be done here? Which is the safer side? To attach or not to attach?
Not to attach. Do not buy a paid ticket, do not pay for the hotel. These checklists are generic and cover for a wide range of cases and not just the standard visitor visa. It is absolutely fine to have some check boxes not checked. For example if you were applying for Transit you would need a confirmed ticket etc.
Section 4: documents you should not send unless specifically requested
Reference: Visitor: Supporting documents guide
However a tour is not just a ticket. It is actually a plan. Share that plan with them. For example if you plan to go for 6 days in November then for the actual travel dates get some ticket reservations (unpaid - its fine if they get cancelled) and show them how and when you plan to go to and back from the UK.
Here is some official text to support my assesment
For visa applications, visitors are not required to provide an itinerary, but you should normally expect the applicant to have some plans for their stay, and provide information about this on the application form.
At the border, you should expect the applicant to be able to answer questions on what they plan to do
Source: Visit guidance - Published for Home Office staff on 14 June 2017
Obviously if you do have letter of Invitation then you must present it and provide evidence of sponsor's immigration status in the UK that's self explanatory.
If you do buy tickets and pay for hotels and provide those to them before securing a visa for the UK you will actually be making your application weaker, not stronger.